Ketosis: What It Is, the Science Behind It, and When It Works Best
Understanding the Pros and Cons of Ketosis, Fasting, and Metabolic Flexibility
Ketosis works—until it doesn’t. Some people experience steady energy, clear thinking, improved blood sugar, and a sense that their metabolism is finally working with them. Others feel depleted, anxious, wired, or stuck despite following the rules closely.
These different outcomes aren’t random, and they’re not a reflection of willpower or discipline. They reflect how ketosis shifts cellular energy production, stress signaling, hormone balance, and nutrient demands in the body. When those shifts are supportive, ketosis can be a powerful therapeutic tool. When they’re mismatched to the individual, the same approach can backfire.
Understanding when ketosis helps—and when it creates strain—requires moving beyond diet rules and into metabolic physiology. From this perspective, ketosis isn’t a lifestyle or a rigid prescription; it’s a flexible strategy that can be applied with precision, cycled intelligently, and adapted to the body’s changing needs over time.
What Is Ketosis?
Ketosis is a natural metabolic state in which the body shifts from relying on glucose (sugar) as its primary fuel to burning fat for energy. When carbohydrate intake drops, the liver converts fatty acids into ketone bodies—primarily beta-hydroxybutyrate (BHB), acetoacetate, and acetone—which then supply energy to the brain, muscles, and other organs. (1)
This metabolic shift is not new or extreme. It evolved as a survival adaptation that allowed humans to function during periods of fasting or food scarcity. Today, ketosis is used more intentionally to support metabolic health, brain function, inflammation regulation, and longevity. (2) For many people seeking sustainable fat loss or improved insulin sensitivity, ketosis works best when it’s part of a broader, supportive strategy rather than a rigid, standalone diet.
In clinical settings, ketogenic or cyclical low-carbohydrate approaches are most effective when hormone balance, thyroid function, stress physiology, and metabolic flexibility are all considered together.
This is why ketosis is typically guided through a functional medicine lens, where decisions are based on physiology rather than rules. In many cases, outcomes are further refined using objective data to ensure ketosis is supporting—rather than depleting—the individual.
Ketosis, Fasting, and Metabolic Flexibility
Fasting naturally induces ketosis by lowering glycogen stores and insulin levels, signaling the body to shift toward burning fat for energy. For some people, this transition feels steady and supportive. For others, it can feel draining or disruptive. Much of that difference comes down to timing, stress load, and hormone balance—not fasting itself.
→ Weight Loss & Metabolic Health
When fasting is paired thoughtfully with a clean, nutrient-dense ketogenic diet, it can help train the body toward metabolic flexibility—the ability to switch between fat and glucose efficiently as needs change. This flexibility, rather than staying in constant ketosis, is what supports sustainable energy, resilience, and long-term metabolic health.
Benefits of Fasting and Ketosis
When applied intentionally, fasting and ketosis influence multiple core systems involved in energy production, metabolic regulation, and cellular repair. These benefits don’t come from calorie restriction alone, but from how shifting fuel sources changes signaling pathways throughout the body.
Cellular Renewal (Autophagy)
Periods of fasting activate autophagy, the body’s built-in cellular recycling process. During autophagy, damaged proteins and dysfunctional cellular components are broken down and cleared away, making room for healthier regeneration. This process plays a key role in longevity, immune resilience, and tissue repair, and is one reason fasting has been associated with improved cellular aging markers. (4)
Mitochondrial Efficiency
Ketosis supports mitochondrial function by providing a more efficient fuel source than glucose. Ketones generate energy with less oxidative stress, allowing cells to produce ATP more cleanly and reliably. Over time, this can improve cellular resilience, reduce fatigue, and enhance the body’s ability to meet energy demands—especially in metabolically stressed states. (5)
Improved Insulin Sensitivity
Both fasting and ketosis lower circulating insulin levels, giving insulin receptors a chance to reset. This improves insulin sensitivity and stabilizes blood sugar regulation, which is particularly important for individuals with insulin resistance, prediabetes, or metabolic syndrome. Rather than forcing blood sugar down, these approaches help restore more normal metabolic signaling. (6)
Hormone Regulation
Fasting and ketogenic states influence key hormones involved in repair and metabolism. Growth hormone secretion increases during fasting, supporting tissue repair and fat metabolism. In appropriate contexts, testosterone signaling may also improve, particularly when insulin resistance and chronic inflammation are reduced. These effects depend heavily on adequate nutrition and stress balance. (7)
Brain Health
Ketones provide a stable, efficient fuel source for the brain and increase levels of brain-derived neurotrophic factor (BDNF), a molecule essential for neuroplasticity, learning, and cognitive resilience. This is one reason ketogenic strategies have been explored in neurological conditions and cognitive decline, as well as for mental clarity and focus in everyday life. (8)
Potential Downsides
While fasting and ketosis offer real metabolic benefits, they can also create strain when applied too aggressively or without regard for individual physiology. These approaches work best as tools—not mandates—and understanding their limits is just as important as understanding their advantages.
Excessive fasting or prolonged calorie restriction can activate the stress response, increasing cortisol output and placing additional demand on the adrenal system. Over time, this stress signaling may suppress thyroid function, slow metabolic rate, and contribute to symptoms such as fatigue, cold intolerance, or stalled progress. (9)
Women, in particular, tend to respond best to cyclical fasting approaches that respect hormonal rhythms rather than daily or prolonged fasting. Estrogen, progesterone, and cortisol interact closely with energy availability, and overly rigid fasting schedules can disrupt this balance, especially during times of high stress or intense training.
→ Hormone & Metabolic Optimization
Long-term deep ketosis or chronic under-eating can also lead to nutrient insufficiency, low energy, mood changes, and hormonal imbalance if not carefully monitored. Rather than enhancing resilience, these patterns may leave the body feeling depleted and stuck. (10)
As Paul Saladino and other functional medicine clinicians emphasize, the goal isn’t to stay in ketosis indefinitely. The goal is metabolic flexibility—the ability to move smoothly between fat and carbohydrate metabolism based on energy needs, stress levels, activity, and season.
When flexibility is prioritized, fasting and ketosis can support health. When rigidity takes over, the same strategies can work against the body instead of with it.
The Benefits of Ketosis
When ketosis is well tolerated and appropriately timed, it can offer meaningful benefits beyond short-term weight loss. These effects come from how ketones influence energy production, inflammation, and cellular signaling—not from carbohydrate restriction alone.
Sharper Mental Clarity
Ketones provide a steady, efficient fuel source for the brain, often leading to more consistent focus and mental clarity. Unlike glucose, which can fluctuate with meals and stress, ketones deliver stable energy that supports cognitive performance without the highs and crashes many people experience on a carb-heavy diet. (11)
Steady Energy
By shifting the body away from rapid glucose cycling, ketosis can reduce energy swings throughout the day. Many people notice fewer crashes between meals and more sustained physical and mental stamina once fat adaptation is established.
Better Blood Sugar Control
Ketosis lowers circulating glucose and insulin demand, helping reduce fasting glucose, A1c, and insulin resistance. For individuals with metabolic dysfunction, this can be a powerful tool for improving blood sugar regulation and reducing long-term disease risk—when applied thoughtfully and monitored appropriately. (12)
Anti-Inflammatory and Longevity Support
Ketones act as signaling molecules that influence pathways involved in cellular repair and stress resistance, including AMPK and Nrf2. Activation of these pathways is associated with improved detoxification capacity, reduced oxidative stress, and mechanisms linked to healthy aging. (13)
Neurological Protection
The ketogenic diet has long been used therapeutically in epilepsy and is increasingly studied for its potential role in neurodegenerative conditions such as Alzheimer’s, Parkinson’s, and multiple sclerosis. By providing an alternative fuel source and reducing neuroinflammation, ketosis may help support brain resilience in vulnerable states. (14)
Keto Flu: Why It Happens and What It Really Means
During the first few days or weeks of starting a ketogenic diet, many people experience what’s commonly referred to as the “keto flu.” (15) For some, it shows up as mild fatigue or fogginess. For others, it can feel discouraging enough to make them question whether ketosis is the right approach at all.
Common symptoms include:
Fatigue or low energy
Brain fog, mood swings, or irritability
Headaches or dizziness
Muscle cramps or palpitations
Nausea or sleep disruption
Physiologically, these symptoms reflect a transition period. As the body shifts from burning glucose to relying more heavily on fat and ketones for energy, insulin levels drop. This signals the kidneys to excrete more sodium, potassium, and magnesium, often leading to electrolyte depletion and dehydration. At the same time, glycogen stores are reduced, removing a readily available fuel buffer. Together, these changes can temporarily leave the body feeling sluggish, foggy, or out of balance.
Importantly, the “keto flu” is not a required or healthy part of metabolic adaptation. In most cases, it signals that the transition is happening too abruptly or without adequate support—particularly electrolytes, calories, or fat intake. In functional medicine, we view this not as failure, but as metabolic feedback that the body needs a gentler approach.
Common Causes of a Difficult Transition
Rapid carbohydrate restriction without allowing time for fat adaptation
Electrolyte depletion from increased urination and sodium loss
Insufficient dietary fat—especially medium-chain fats—to adequately fuel mitochondria
Adrenal or thyroid stress from stacking fasting with aggressive low-carbohydrate intake
Overtraining, poor sleep, or chronic stress, which elevate cortisol and impair fat utilization
Because stress hormones and thyroid signaling play a central role in how the body adapts to ketosis, symptoms of the keto flu often overlap with broader patterns of stress intolerance or hormonal strain.
When carbohydrate restriction is layered on top of high life stress, intense training, or inadequate recovery, the body may struggle to adapt smoothly—regardless of how “perfect” the diet looks on paper.
How MCT and Coconut Oil Can Help Ease the Transition
Medium-chain triglycerides (MCTs)—found abundantly in coconut oil—are unique fats that can make the transition into ketosis far smoother and more sustainable, especially for people who feel depleted or discouraged early on.
Unlike long-chain fatty acids, which require bile acids, pancreatic enzymes, and the L-carnitine shuttle to enter the mitochondria for oxidation, MCTs completely bypass this transport system.
That difference is crucial during the early stages of ketosis. When you’re not yet fat-adapted, mitochondria are often inefficient at transporting long-chain fats across the mitochondrial membrane. This bottleneck—the carnitine shuttle—can lead to fatigue, sluggishness, and classic “keto flu” symptoms, because the body hasn’t yet learned how to efficiently produce ketones from stored fat. (16)
MCTs, however, skip this step entirely. They’re absorbed directly through the portal vein, delivered straight to the liver, and rapidly converted into ketone bodies—providing immediate energy for both the brain and muscles. (17) This is why many people feel clearer and more stable shortly after introducing MCTs, even before full fat adaptation occurs.
Benefits of MCT and Coconut Oil During Keto Adaptation
Immediate Energy Boost
MCTs are rapidly converted into ketones, offering instant cellular fuel during a phase when energy often feels low or inconsistent.
Enhanced Brain Function
They provide an alternative energy source for neurons, which can noticeably improve focus and mental clarity during early ketosis.
Bypass Metabolic Bottlenecks
Because MCTs don’t rely on the carnitine shuttle, they deliver energy efficiently even when long-chain fat oxidation is still sluggish.
Reduce Keto Flu Symptoms
By improving energy availability and mitochondrial fuel supply, MCTs can help minimize fatigue, brain fog, and the sense of “dragging” many people experience early on.
Train Fat Metabolism
With regular use, MCTs help upregulate mitochondrial enzymes, easing the transition into more efficient, sustained fat-burning.
Clinical Tip:
Start slowly—1 teaspoon of MCT oil once or twice daily (often in coffee or tea)—and gradually increase to 1–2 tablespoons as tolerated. Too much too quickly may cause loose stools or nausea. For sensitive individuals, virgin coconut oil offers a gentler starting point while still providing key ketogenic fatty acids (C8 and C10).
Functional Insight:
MCTs act as training wheels for your mitochondria. By bypassing the carnitine shuttle, they bridge the energy gap between glucose dependence and full fat adaptation—helping you move into ketosis with less stress and fewer setbacks.
Functional Strategies to Prevent or Ease Keto Flu
For most people, the discomfort of the keto flu isn’t a sign that ketosis is wrong—it’s a sign that the transition needs more support. These strategies focus on helping the body adapt gradually and safely, rather than forcing it into a metabolic shift too quickly.
Transition gradually
Lower carbohydrates over 2–3 weeks while increasing clean fats such as avocado, olive oil, coconut, and MCTs. This gives enzymes, mitochondria, and hormone signaling time to adjust, reducing stress on the system.
Replenish minerals
As insulin drops, the kidneys excrete more sodium and trace minerals. Using quality salt or mineral support like Quinton Isotonic or Hypertonic helps maintain electrolyte balance and prevent headaches, fatigue, and lightheadedness.
Hydrate deeply
Aim for 3–4 liters of mineralized, filtered water per day. Increased urination is common early in ketosis, and dehydration alone can amplify many keto flu symptoms if fluid and minerals aren’t replaced.
Eat enough fat
Avoid going low-carb and low-fat at the same time. During adaptation, mitochondria need adequate fuel to learn how to burn fat efficiently. Under-eating can stall progress and increase fatigue rather than speed results.
Support adrenals and thyroid
Prioritize sleep, circadian rhythm, stress reduction, and adequate calories. When the stress response is already elevated, adding aggressive carbohydrate restriction can push the body into conservation mode instead of adaptation.
Why this matters
Ketosis works best when the body feels supported, not threatened. Addressing hydration, minerals, fuel, and recovery allows metabolic adaptation to occur with far less friction—often eliminating the need to “push through” uncomfortable symptoms altogether.
Monitoring Ketosis: Why Testing Matters
Tracking your ketone levels helps you understand how your body responds to diet and fasting. Not everyone enters or maintains ketosis at the same threshold — stress, sleep, and carb intake can all influence it.
Methods of Ketone Testing
Urine Strips: Inexpensive but unreliable once fat-adapted (measure acetoacetate, not BHB).
Breath Meters: Convenient but less precise.
Blood Monitors: The gold standard — measure beta-hydroxybutyrate (BHB), the main circulating ketone.
For patients who want objective data rather than guesswork, blood ketone testing is often paired with Advanced Functional Lab Testing to assess metabolic trends alongside glucose, insulin, and stress markers.
Monitoring Ketosis: Why Testing Matters
Tracking ketone levels can be helpful, not because there’s a single “perfect number,” but because it shows how your body responds to diet, fasting, stress, and sleep. Two people can eat the same foods and follow the same plan, yet produce very different ketone levels. Testing removes guesswork and helps distinguish what’s working from what’s quietly creating strain.
Not everyone enters or maintains ketosis at the same threshold. Factors such as stress load, sleep quality, training intensity, and carbohydrate timing all influence ketone production—sometimes more than food alone.
Methods of Ketone Testing
Urine Strips
Inexpensive and easy to use, but less reliable over time. These measure acetoacetate, which often declines once the body becomes fat-adapted, even if ketosis is still present.
Breath Meters
Convenient and non-invasive, but more variable and less precise, particularly for tracking trends.
Blood Monitors
Considered the gold standard. Blood testing measures beta-hydroxybutyrate (BHB), the primary circulating ketone used by the brain and muscles, and provides the most accurate picture of metabolic state.
For individuals who want objective feedback rather than symptoms alone, blood ketone testing is often paired with broader metabolic data to see how ketosis fits into the larger physiological picture.
→ Advanced Functional Lab Testing
Keto-Mojo: A Practical Tool for Home Monitoring
At Denver Sports & Holistic Medicine, we often recommend Keto-Mojo as a practical option for people who want reliable, at-home tracking of both ketones and glucose without unnecessary complexity.
Why Keto-Mojo Is Useful
Dual Measurement
Tracks both blood glucose and BHB, allowing calculation of the Glucose Ketone Index (GKI), which can offer insight into metabolic efficiency and fuel utilization.
Clinical Accuracy
FDA-approved and validated in research, making it suitable for clinical and personal use.
Simple Data Tracking
Syncs with the Keto-Mojo app and integrates with platforms like Apple Health or Cronometer, making it easier to observe patterns over time rather than focusing on isolated readings.
Functional Versatility
Useful for people exploring fasting, metabolic health, longevity strategies, or therapeutic ketosis under supervision.
Cost-Effective for Long-Term Use
Test strips are generally more affordable than many alternatives, which matters for ongoing tracking.
Target Ketone Ranges
Nutritional ketosis: ~0.5–3.0 mmol/L BHB
Therapeutic ketosis: ~3–5 mmol/L BHB, used selectively and under clinical supervision
These ranges are guides, not goals. Higher numbers are not inherently better, and context—symptoms, energy, hormones, and stress response—always matters more than the number alone.
Why the Keto Diet Can Backfire: Cortisol, Gluconeogenesis, and Blood Sugar Spikes
For some people, ketogenic diets improve blood sugar and energy. For others, they do the opposite—raising fasting glucose, increasing anxiety, or creating a “wired but tired” feeling. When this happens, it’s rarely about carbohydrates alone. It’s usually about stress physiology.
Low Carbohydrate Intake Can Trigger a Stress Response
When carbohydrate intake drops very low, the body may interpret this as an energy deficit or starvation signal—especially if the change is abrupt or layered on top of existing stress. In response, the hypothalamic-pituitary-adrenal (HPA) axis activates, releasing cortisol and, to a lesser degree, adrenaline (epinephrine).
These hormones are not harmful by default. They exist to protect the brain and maintain blood sugar during fasting or perceived scarcity. Cortisol helps do this by:
Stimulating gluconeogenesis—the production of new glucose in the liver from amino acids, glycerol (from fat breakdown), and lactate when glycogen stores are low
Increasing lipolysis (fat breakdown)
Reducing glucose uptake in muscle to spare glucose for the brain
As a result, even when carbohydrate intake is extremely low, cortisol can raise fasting blood sugar by signaling the liver to produce more glucose.
Gluconeogenesis Can Keep Blood Sugar Elevated
In nutritional ketosis, a moderate level of gluconeogenesis is both normal and necessary. The body still needs glucose for certain tissues, and the liver is designed to supply it.
Problems arise when cortisol remains elevated due to chronic stress, excessive fasting, or prolonged calorie restriction. In that context, gluconeogenesis can become excessive rather than adaptive.
This can lead to:
Persistently elevated fasting glucose (often 90–110 mg/dL or higher)
Stalled ketone production despite strict low-carb intake
Fatigue, anxiety, irritability, or sugar cravings—even when technically “in ketosis”
This is why some people see paradoxically higher morning glucose readings on keto, despite careful adherence. (18)
Chronic Cortisol Elevation Blocks Fat Adaptation
Sustained cortisol signaling also interferes with mitochondrial efficiency and fuel flexibility.
When the stress response dominates:
The body prioritizes glucose over fat as an emergency fuel
Insulin sensitivity worsens over time
Muscle protein is broken down to supply glucose
Thyroid conversion (T4 → T3) slows, reducing metabolic rate
Physiologically, the body shifts out of a state of repair and adaptation and into fight-or-flight survival mode. In this state, fat-burning becomes inefficient—not because ketosis “failed,” but because stress chemistry is overriding metabolic flexibility. (19,20)
Other Triggers That Can Exacerbate Cortisol on Keto
Several factors can amplify this response, especially when combined:
Overtraining while in deep ketosis (low glycogen = higher stress signaling)
Under-eating calories or protein, which reinforces a starvation signal
Sleep deprivation or circadian rhythm disruption
Extended fasting without strategic refeed periods
Pre-existing adrenal dysfunction or HPA axis dysregulation
Over time, these factors compound, driving morning blood sugar spikes and even insulin resistance—the opposite of what most people are trying to achieve with a ketogenic approach.
How to Fix It: Functional Medicine Strategies
When ketosis starts to raise blood sugar or feel depleting, the solution is rarely to restrict further. More often, it’s about restoring balance so the body no longer perceives a threat. From a functional medicine perspective, these adjustments help calm stress signaling and allow metabolic flexibility to return.
Add Strategic Carbohydrate Refeeds
Including one to two carbohydrate-containing meals per week—such as root vegetables, fruit, or squash—can help replenish glycogen and support leptin and thyroid signaling. Rather than “undoing” progress, strategic refeeds often improve energy, sleep, and metabolic responsiveness over time.
Prioritize Sleep and Stress Reduction
Sleep is one of the most powerful regulators of cortisol. Even short-term sleep deprivation can raise cortisol by 30–40%, offsetting the metabolic benefits of ketosis. Practices such as breathwork, meditation, acupuncture, and targeted adaptogens (ashwagandha, rhodiola, holy basil) can help lower stress load and improve recovery.
Support Adrenals and Electrolytes
Adequate minerals are essential when insulin levels are low. Using mineral-rich sea salt, magnesium, and potassium—often through trace minerals or products like Quinton—helps stabilize blood sugar, reduce fatigue, and support adrenal signaling during metabolic transitions.
Track Your Pattern
Tools like blood ketone testing, glucose monitoring, or continuous glucose monitors (CGMs) can reveal patterns that symptoms alone may miss. Many people notice higher morning glucose that mirrors normal cortisol rhythms (the “dawn phenomenon”), offering valuable insight into stress-driven rather than food-driven responses.
Personalize Your Approach
For individuals with adrenal fatigue, thyroid dysfunction, or high chronic stress, a cyclical ketogenic plan or a low-carbohydrate Mediterranean-style approach is often more supportive and sustainable than strict, continuous ketosis.
Key Clinical Insight
“If your blood sugar rises on keto, it’s not always the food—it’s often the stress chemistry.”
The answer isn’t greater restriction or more discipline. It’s restoring metabolic balance, supporting stress physiology, and choosing an approach that works with your body rather than against it.
Keto and Cancer: Supporting the Metabolic Terrain
One of the most compelling therapeutic applications of ketosis is in the context of cancer metabolism. Rather than viewing cancer solely as a genetic condition, growing research—and long-standing insight from metabolic oncology—recognizes cancer as a disease shaped by cellular energy dysfunction.
This perspective is explored more deeply in How Metabolic Health Shapes Cancer Prevention and Treatment, which examines how targeting glucose dependence, insulin signaling, and mitochondrial dysfunction may help support conventional cancer therapies.
Emerging evidence supports what functional medicine has long observed: many cancers thrive in environments marked by impaired mitochondrial function, elevated insulin signaling, and altered glucose metabolism. Addressing this metabolic terrain can meaningfully influence how the body responds to disease and treatment.
The Metabolic Theory of Cancer
Healthy cells are metabolically flexible. They can shift between burning glucose and fat depending on availability and demand. Many cancer cells, however, lose this flexibility and become heavily reliant on aerobic glycolysis—a phenomenon known as the Warburg effect—meaning they depend primarily on glucose (and glutamine) for energy, even when oxygen is present.
By reducing glucose availability through ketosis, it may be possible to exploit this metabolic vulnerability in cancer cells while simultaneously nourishing healthy cells with ketones, which they can use efficiently for ATP production and cellular repair. (21,22,23)
Put simply: ketosis may help deprive cancer cells of their preferred fuel while strengthening mitochondrial function in healthy tissue.
Potential Benefits of a Therapeutic Ketogenic Diet
When used as an adjunct and under supervision, therapeutic ketosis may offer several metabolic advantages in cancer care:
Lower circulating glucose and insulin, potentially reducing growth signals such as IGF-1 that support tumor proliferation. (24)
Enhanced mitochondrial resilience and reduced oxidative stress in healthy cells. (25)
Improved sensitivity of cancer cells to conventional therapies like chemotherapy and radiation by increasing oxidative vulnerability. (26)
Better energy, mood, and weight stability for some patients during treatment.
These effects are not guaranteed and depend heavily on individual physiology, disease state, and treatment context.
Clinical Insights: Not a One-Size-Fits-All Approach
While ketogenic therapy shows promise in cancer care, it must be personalized and medically supervised. Certain patients—particularly those with adrenal dysfunction, thyroid imbalance, or cachexia (cancer-related weight loss)—may not tolerate deep or prolonged ketosis well.
In these cases, a modified or cyclical ketogenic approach, with thoughtful carbohydrate and protein adjustments, often provides better balance and sustainability.
At Denver Sports & Holistic Medicine, we use functional lab testing, nutritional genomics, and metabolic assessments to tailor each plan carefully—supporting mitochondrial health, detoxification capacity, and hormonal stability alongside therapeutic ketosis.
Cautions and Considerations
Avoid extreme calorie restriction or prolonged fasting without medical guidance during active cancer treatment.
Ensure adequate micronutrient and antioxidant support, including magnesium, selenium, zinc, B-vitamins, and CoQ10.
Pair ketosis with gentle detoxification and mitochondrial support strategies (such as NAD precursors, PQQ, or sulforaphane).
Monitor progress through lab testing, ketone and glucose tracking, and ongoing clinician oversight.
Key Takeaway
Ketosis is not a cancer cure—but it can be a powerful metabolic tool that shifts the body’s terrain toward resilience and support. When guided by a practitioner trained in metabolic medicine, a ketogenic approach may complement conventional care, reduce treatment burden, and improve quality of life for select patients.
Paul Saladino’s Animal-Based Perspective
Dr. Paul Saladino, once a strict carnivore advocate, now emphasizes metabolic cycling—alternating between fat- and carbohydrate-based metabolism to support thyroid function, hormone balance, and long-term resilience. His philosophy reflects a broader functional medicine principle:
“Ketosis is a tool, not a prison. Flexibility is health.”
By encouraging seasonal inclusion of clean carbohydrates such as fruit or raw honey, this approach aims to support glycogen balance, circadian rhythm, and thyroid signaling—reinforcing the idea that metabolic flexibility, not perpetual restriction, is the ultimate goal. (18)
Who Should Consider Ketosis or Fasting?
May be beneficial for individuals with:
Insulin resistance, prediabetes, or type 2 diabetes
Neurological conditions or age-related cognitive decline
Chronic inflammation, autoimmune activity, or mitochondrial dysfunction
Weight loss goals or longevity-focused metabolic protocols
Use caution or individualized guidance if you have:
Adrenal dysfunction or thyroid disorders
Low body weight, high training demands, or athletic energy requirements
Pregnancy or are breastfeeding
Functional Medicine Perspective
At Denver Sports & Holistic Medicine, we view ketosis, fasting, and ketone monitoring as part of a precision metabolic strategy — tailored to each person’s unique physiology, hormones, and stress response.
Through advanced lab testing (glucose, insulin, thyroid, cortisol, and mitochondrial markers) and real-time tracking, we help patients achieve fat adaptation, metabolic flexibility, and sustainable energy — without deprivation or burnout.
Key Takeaway
Ketosis and fasting are powerful metabolic therapies when personalized and cycled intelligently. They can enhance mental clarity, energy, and longevity — but the key is balance and support.
Use ketosis to heal — and metabolic flexibility to thrive.
Personalizing Ketosis for Your Metabolism
Ketosis and fasting can be powerful tools—but only when they work with your body, not against it. Hormones, stress, sleep, thyroid function, and life demands all shape how your metabolism responds, which is why no single diet approach works the same for everyone.
→ Functional & Integrative Medicine
If you’re curious whether ketosis or fasting could support your energy, focus, or long-term health—or if you’ve tried these approaches before and felt worse—a conversation with Dr. Martina Sturm can help you make sense of what your body may be asking for and what steps make sense next.
Request a free 15-minute consultation with Dr. Martina Sturm at Denver Sports & Holistic Medicine to begin restoring balance, energy, and resilience from the inside out.
Frequently Asked Questions About Ketosis & Fasting
If you’re considering a ketogenic or fasting approach, it’s natural to have questions about safety, duration, and long-term impact. Below, we’ve answered some of the most common questions we hear at Denver Sports & Holistic Medicine from patients exploring ketosis for energy, weight loss, or metabolic health.
These FAQs combine functional medicine insight with evidence-based research to help you apply ketosis safely, avoid common pitfalls like the “keto flu,” and understand when it’s time to transition back toward metabolic flexibility—the ability to burn both fat and carbohydrates efficiently.
What is ketosis, and how does it work?
Ketosis is a natural metabolic state in which your body burns fat instead of glucose for energy. When carbohydrates are restricted, the liver produces ketones (beta-hydroxybutyrate, acetoacetate, and acetone), which fuel the brain and muscles efficiently while reducing inflammation and stabilizing blood sugar.
What causes the “keto flu”?
The keto flu occurs when the body transitions too quickly into ketosis, leading to electrolyte loss, dehydration, and low energy. Common symptoms include fatigue, brain fog, and muscle cramps. It’s usually a sign that carbohydrate restriction was too abrupt or that fat intake and mineral support are inadequate.
How can I prevent or fix the keto flu?
Transition gradually over 2–3 weeks, increase electrolyte intake (especially sodium, magnesium, and potassium), and include MCT or coconut oil to provide fast fuel while your body adapts. MCTs bypass the L-carnitine shuttle, providing immediate ketone energy and easing the adjustment phase.
What makes MCT oil different from other fats?
Unlike long-chain fats, MCTs don’t require bile acids or the carnitine shuttle to enter mitochondria. They’re absorbed directly through the portal vein and rapidly converted into ketones by the liver, providing a quick, clean energy source that supports brain and metabolic function.
How do I know if I’m in ketosis?
Ketone levels can be measured using urine strips, breath meters, or blood testing. The most accurate method is blood testing for beta-hydroxybutyrate (BHB). At Denver Sports & Holistic Medicine, we often recommend blood-based tracking for precise insight into metabolic trends.
How long should I stay in ketosis?
Ketosis isn’t meant to be permanent for everyone. Short cycles (typically 2–8 weeks) can help reset metabolism, but remaining in deep ketosis long term may negatively affect thyroid and hormone balance. Cycling between fat- and carbohydrate-based metabolism is often more supportive of long-term metabolic flexibility.
Who should avoid or modify the ketogenic diet?
Individuals with adrenal fatigue, hypothyroidism, pregnancy, or chronic stress often require a more moderate or cyclical approach. In functional medicine, ketosis is personalized using lab data, hormone patterns, and metabolic resilience rather than applied rigidly.
What’s the ideal ketone range for health benefits?
For most people, nutritional ketosis begins around 0.5 mmol/L and provides benefits up to approximately 2–3 mmol/L of BHB. Therapeutic ketosis—used in specific neurological or cancer-related protocols—may range from 3–5 mmol/L and should be done under clinical supervision.
What foods support healthy ketosis?
A well-formulated ketogenic diet emphasizes whole-food fats (avocados, olive oil, coconut), pasture-raised eggs, grass-fed meats, clean proteins, and low-starch vegetables. Highly processed “keto” snacks with seed oils or sugar alcohols should be avoided, as they can increase inflammation and disrupt gut balance.
How long can a ketogenic diet be done safely?
The ideal duration depends on your goals, health status, and hormone balance. For most individuals, short to moderate cycles (4–12 weeks) are safe and effective for improving insulin sensitivity, fat loss, and inflammation.
Long-term strict ketosis may lower thyroid hormone (T3), reduce leptin, and raise cortisol—especially in women, athletes, or those under stress. This is why cyclical or targeted keto approaches tend to be safer and more sustainable.
At Denver Sports & Holistic Medicine, we personalize duration and cycling using lab testing, including thyroid, insulin, cortisol, and nutrient markers.
What are signs it may be time to come out of ketosis?
If ketosis feels depleting rather than energizing, it may be time to reintroduce carbohydrates. Common signs include fatigue, poor sleep, cold intolerance, menstrual irregularities, irritability, or stalled weight loss.
These signals often indicate a need for carbohydrate support to restore thyroid function, leptin signaling, and glycogen stores. Strategic refeeding with nutrient-dense carbohydrates can improve metabolism, mood, and resilience.
Why does blood sugar sometimes rise on keto despite very low carb intake?
This paradox is often driven by stress physiology rather than carbohydrate intake. Excessive carb restriction or prolonged fasting can increase cortisol, which signals the liver to produce glucose through gluconeogenesis.
In functional medicine, the solution is not further restriction but restoring balance through improved sleep, stress reduction, strategic carb refeeds, and adequate fuel to stabilize cortisol and blood sugar naturally.
FAQ Summary
A ketogenic diet can be a powerful therapeutic tool when applied intentionally and personalized to your body’s needs. Whether ketosis is used for insulin resistance, inflammation, brain health, or performance, the key is balance, monitoring, and strategic cycling.
At Denver Sports & Holistic Medicine, we help patients determine:
How long ketosis is appropriate for their goals
When and how to reintroduce healthy carbohydrates
How to track progress using ketones and glucose
How to support thyroid, adrenal, and mitochondrial health throughout the process
If you’re ready to explore personalized nutrition and metabolic testing, scheduling a consultation can help you design a sustainable path toward long-term energy and metabolic resilience.
Resources
ScienceDirect – The Effects of Ketone Bodies in Pathological Conditions: Ketosis, Ketogenic Diet, Redox States, Insulin Resistance, and Mitochondrial Metabolism
PubMed – The Effect of a Low-Carbohydrate, Ketogenic Diet Versus a Low-Glycemic Index Diet on Glycemic Control in Type 2 Diabetes Mellitus
PubMed – Fasting, Circadian Rhythms, and Time-Restricted Feeding in Healthy Lifespan
PMC – The Impact of Diet Upon Mitochondrial Physiology (Review)
PMC – The Effects of Ketogenic Diet on Insulin Sensitivity and Weight Loss: Which Came First, the Chicken or the Egg?
PubMed – Ketogenic State Improves Testosterone Serum Levels: Results from a Systematic Review and Meta-Analysis
PubMed – The Ketogenic Diet as a Treatment Paradigm for Diverse Neurological Disorders
PMC – The Influence of Extended Fasting on Thyroid Hormone: Local and Differentiated Regulatory Mechanisms
Journal Article – Effects of Very Low-Calorie Ketogenic Diet on the Hypothalamic–Pituitary–Adrenal Axis and Renin–Angiotensin–Aldosterone System
PubMed – Ketone Bodies as Signaling Metabolites
PubMed – Beyond Weight Loss: A Review of the Therapeutic Uses of Very-Low-Carbohydrate (Ketogenic) Diets
PMC – Key Signaling Pathways in Aging and Potential Interventions for Healthy Aging
PMC – The Therapeutic Role of Ketogenic Diet in Neurological Disorders
Journal Article – The Ketogenic Diet: Evidence for Optimism but High-Quality Research Needed
PubMed – Medium-Chain Triglycerides: An Update
PubMed – Short- and Medium-Chain Fatty Acids in Energy Metabolism: The Cellular Perspective
PubMed – Medium-Chain Triglycerides Are Advantageous in Promoting Weight Loss Although Not Beneficial to Exercise Performance
Journal Article – New Insights into the Utilization of Medium-Chain Triglycerides by the Neonate: Observations from a Piglet Model
PubMed – Fuel Metabolism in Starvation
PubMed – Stress Hormones: Physiological Stress and Regulation of Metabolism
Journal Article – Hormonal Exercise Response Model (HERM): A Conceptual Framework of Endocrine Reactivity to the Physical Stress of Exercise
PubMed – Cancer as a Metabolic Disease: Implications for Novel Therapeutics
Journal Article – Targeting Insulin Inhibition as a Metabolic Therapy in Advanced Cancer: A Pilot Safety Study
PubMed – Beneficial Effects of Ketogenic Diets for Cancer Patients: A Realist Review with Focus on Evidence and Confirmation
PubMed – Effect of Ketogenic Diets on Insulin-Like Growth Factor (IGF-1) in Humans: A Systematic Review and Meta-Analysis
PMC – Ketogenic Diet Decreases Oxidative Stress and Improves Mitochondrial Respiratory Complex Activity
PMC – Ketogenic Diets as an Adjuvant Cancer Therapy: History and Potential Mechanisms
Podcast / Interview – Why Paul Saladino, MD Quit a 100% Carnivore Diet: Impacts of Cholesterol and the Value of Insulin