Ketosis isn't a diet. It's a metabolic state and most of us have forgotten how to get there
When most people hear the word "ketosis," they picture butter coffee, bacon-wrapped everything, and a strict set of rules about what you're allowed to eat. The ketogenic diet has a strong cultural presence, and it tends to dominate the conversation. But the diet and the metabolic state it's named after are not the same thing and conflating them has caused a lot of people to either dismiss ketosis entirely or pursue it in a way that isn't sustainable or even necessary.
Ketosis is something your body has always been capable of. It's a natural metabolic state that humans would have entered regularly throughout most of our evolutionary history during overnight fasts, between meals, during periods of physical exertion, and during seasons when carbohydrate-dense food simply wasn't available. The question isn't whether ketosis is "healthy." It's why so many of us have lost the ability to get there at all and what that's costing us metabolically.
What ketosis actually is and what it isn't
Ketosis is a state in which your liver produces ketone bodies primarily beta-hydroxybutyrate, acetoacetate, and acetone from fatty acids, which your cells then use as fuel in place of glucose. It happens when carbohydrate and glycogen stores are sufficiently depleted that the body shifts toward fat as its primary energy source.
This is not the same as ketoacidosis, which is a medical emergency seen primarily in people with type 1 diabetes where ketone levels reach dangerously high concentrations (typically 15–25 mmol/L) in the context of insulin deficiency. Nutritional ketosis sits between roughly 0.5 and 3.0 mmol/L a physiologically normal state, well within the body's regulatory capacity, and entirely different in mechanism and risk profile from diabetic ketoacidosis. The conflation of these two states has unfortunately caused unnecessary fear in both patients and some clinicians.
The ketogenic diet typically defined as less than 20–50g of carbohydrate daily, with high fat (around a 3:1 ratio of fat to protein) and moderate protein is one way to stay in ketosis continuously. But it's not the only way to enter ketosis, and continuous ketosis isn't the goal for everyone. What matters for most people's metabolic health is something different: metabolic flexibility the ability to efficiently use both glucose and ketones as fuel, switching between them as circumstances demand.
Metabolic flexibility: the capacity we've quietly lost
A metabolically flexible person burns glucose when carbohydrates are available and readily shifts to fat burning including mild ketone production when they're not. They can go 12–16 hours without eating and feel reasonably stable. They don't experience intense carbohydrate cravings every 2–3 hours. Their energy doesn't crater mid-afternoon.
A metabolically inflexible person is stuck in glucose-dependence. They require frequent carbohydrate intake to maintain energy and mood. They struggle with extended fasting. Their cells have essentially forgotten how to access fat stores efficiently not because fat isn't there, but because chronically elevated insulin has kept fat locked away, and the machinery for fat oxidation has become underused and sluggish.
This is not a niche problem. It is, by most metabolic health metrics, the dominant state of the modern population. Estimates suggest that over 90% of American adults have at least one marker of metabolic dysfunction, and data from the Public Health Agency of Canada indicates that approximately one in three Canadian adults has pre-diabetes or metabolic syndrome. The majority of these people have no idea.
What's happening with insulin resistance and why it matters
Insulin resistance is the condition in which your cells respond less efficiently to insulin's signal to take up glucose from the bloodstream. In response, the pancreas produces more insulin to compensate, which keeps blood glucose in a manageable range but at the cost of chronically elevated insulin levels (hyperinsulinemia). For years, sometimes decades, blood glucose can look "normal" on a standard fasting glucose test while insulin is running high. By the time a pre-diabetes diagnosis arrives, the underlying metabolic disruption has typically been present for 5,10 or even more years.
Chronically elevated insulin has consequences beyond blood sugar. It promotes fat storage (particularly visceral, abdominal fat), suppresses fat oxidation, drives systemic inflammation, disrupts sex hormone balance (contributing to PCOS and low testosterone), contributes to early menopause, infertility, impairs sleep quality, and is increasingly implicated in cognitive decline. Alzheimer's disease researchers have begun describing it informally as "type 3 diabetes" a term that reflects the growing body of evidence linking insulin resistance and impaired glucose metabolism in the brain to neurodegeneration. A 2005 study in the Annals of the New York Academy of Sciences (de la Monte & Wands) laid early groundwork for this framing, and subsequent research has continued to deepen the association.
The driver of this epidemic is, in large part, a food environment that has made continuous carbohydrate availability the norm ultra-processed foods engineered to be rapidly absorbed and craving-inducing, eating patterns that span 15–16 hours of the day, and the elimination of the metabolic breathing room that our physiology was built around.
Why humans were designed to enter ketosis regularly
For the vast majority of human history, ketosis wasn't a dietary intervention. It was a predictable consequence of life. Overnight fasting of 12–14 hours was the default. Food availability was seasonal. Physical activity was non-optional. The metabolic machinery that produces ketones evolved precisely because periods of low carbohydrate availability were a routine feature of human existence and the brain, the heart, and the muscles needed an efficient backup fuel system.
Ketone bodies are not simply a survival mechanism for starvation. They are, in several respects, a preferred fuel. The brain can derive up to 70% of its energy from ketones when they're available, and does so with greater efficiency than glucose in many contexts. A 2016 review in Neurobiology of Aging (Cunnane et al.) found that ketone metabolism may partially compensate for the impaired glucose uptake seen in the aging brain, with implications for cognitive preservation.
Beta-hydroxybutyrate the primary ketone in nutritional ketosis has also been identified as a signalling molecule in its own right. It inhibits the NLRP3 inflammasome, a key driver of chronic inflammation. It increases BDNF (brain-derived neurotrophic factor), which supports neuronal growth and plasticity. It activates SIRT3, a mitochondrial protein associated with longevity. These are not trivial effects, and they occur at ketone levels achievable through intermittent fasting alone not only through a strict ketogenic diet.
The body was built to use this system. We've simply engineered a food environment that keeps it permanently switched off.
You don't have to go "keto" to benefit from ketosis
This is the practical piece that tends to get lost. Entering a mild state of ketosis does not require eating butter and bacon for every meal, counting net carbohydrates to the gram, or giving up fruit forever. It requires, essentially, giving your glycogen stores time to deplete which happens naturally through a combination of fasting duration, targeted diet and physical activity.
A 12–14 hour overnight fast (finishing dinner at 7pm and eating breakfast at 9am) over a few days depending on the person can move many people into mild ketosis by morning, particularly if dinner was moderate in carbohydrates. However, if you have high fasting insulin, excess body fat, low nutritional markers, low physical activity and low muscle mass, it may take longer than a few days to enter ketosis, it may take weeks - months. Extending that to 16 hours deepens it. Adding morning movement a 30–40 minute walk or workout before eating depletes glycogen further and amplifies the effect. This is a significant part of what intermittent fasting protocols are actually doing metabolically: not "starving" the body, but creating the window of carbohydrate restriction that allows fat oxidation and ketone production to kick in. This is why each person’s case is different and why you should always work with a practitioner who understands Ketosis and safely guiding you to enter it and come out of it.
A lower-carbohydrate dietary pattern not necessarily full ketogenic, but substantially reducing refined carbohydrates, flour, added sugars, and frequent snacking improves insulin sensitivity and makes entering ketosis easier and more reliable. The two approaches compound: a diet lower in refined carbohydrates means glycogen stores deplete more readily during a fast, and ketosis sets in sooner.
For people with significant insulin resistance, more structured approaches including periodic 24–36 hour fasts, a trial of stricter carbohydrate restriction, or a time-restricted eating window may be needed to meaningfully shift the metabolic pattern. These are things to work through with a knowledgeable clinician rather than self-prescribe. However, like I said, this is a case by case scenario, if you are someone who has the lab work that suggests you cannot tolerate a longer fast or lower carbohydrate diets than you should not enter into this! To help examine your blood work you can book an appointment with me and we can go over your lab work together.
What this could look like in practice
In my practice, I don't reflexively recommend a ketogenic diet. For some patients those with significant insulin resistance, metabolic syndrome, or neurological conditions where ketone metabolism may be therapeutic a more structured ketogenic approach makes sense. For many others, the goal is simply to restore metabolic flexibility: to get the body back to a place where it can enter ketosis easily and regularly, and switch back to glucose metabolism smoothly.
What that often looks like practically: extending the overnight fast to 13–15 hours as a consistent baseline, eating to a pattern where snacking between meals is the exception rather than the rule, substantially reducing ultra-processed and refined carbohydrates while keeping whole food carbohydrates (legumes, root vegetables, fruit), and incorporating gentle morning movement in a fasted state several times per week.
We often track progress with fasting insulin (not just fasting glucose), HbA1c, and sometimes ketone monitoring either blood or breath to understand where a patient is metabolically and how their body is responding. Fasting insulin is particularly informative because it identifies insulin resistance years before blood glucose becomes abnormal, giving us time to intervene meaningfully.
The metabolic shift isn't fast. Most patients begin to notice improved energy stability, reduced cravings, and better mental clarity within 4–8 weeks of implementing these changes consistently. Meaningful improvement in fasting insulin typically takes 3–6 months. But the changes, once established, tend to be durable because they represent a genuine restoration of metabolic function rather than a dietary rule that requires willpower to maintain.
Frequently asked questions
Is ketosis safe for everyone? For most healthy adults, mild nutritional ketosis achieved through fasting or dietary modification is safe and well-tolerated. There are specific situations requiring caution or medical supervision: people with type 1 diabetes (where insulin regulation is compromised), those with a history of eating disorders, individuals with certain rare metabolic conditions, and women who are pregnant or breastfeeding. If you have any of these situations, you should not be fasting and should work with a qualified healthcare provider before pursuing fasting or significant carbohydrate restriction.
How do I know if I'm insulin resistant? The most reliable early markers are fasting insulin, HbA1c, fasting glucose, and a waist circumference above 88cm in women or 102cm in men. Many people with insulin resistance have normal fasting glucose which is why that test alone misses most early cases. If you've never had fasting insulin tested, it's worth asking for.
Will eating fat make my cholesterol worse? This depends significantly on the type of fat, your individual genetics, and what you're replacing. For most people, replacing refined carbohydrates with whole food fats improves the HDL-to-triglyceride ratio often dramatically even if LDL rises modestly. Triglyceride levels are one of the most sensitive markers of carbohydrate metabolism; they tend to fall reliably on lower-carbohydrate, higher-fat dietary patterns. That said, lipid response to dietary fat is genuinely individual, and monitoring lipids while making significant dietary changes is reasonable practice.
Can I enter ketosis without intermittent fasting? Yes, though it's slower. A sufficiently low carbohydrate dietary intake will deplete glycogen and induce ketosis over 2–3 days without fasting, which is how a standard ketogenic diet works. Fasting accelerates the process but isn't required. For people who find fasting difficult initially particularly those who are very insulin resistant and experiencing significant blood sugar instability reducing carbohydrate intake first, then gradually extending the overnight fast, is a more comfortable approach.
Does ketosis help with weight loss, or is it just water weight at first? Both things are true. The initial 1–3kg of weight loss on any carbohydrate-restricted approach is largely water and glycogen depletion each gram of glycogen is stored with approximately 3g of water. Longer-term, the mechanisms that support fat loss include improved insulin sensitivity (which allows fat to be mobilized from storage), reduced appetite (ketones and higher protein intake are more satiating than refined carbohydrates), and potentially improved mitochondrial function. The research on long-term ketogenic diet versus other dietary approaches for weight maintenance is mixed; the metabolic flexibility framework suggests that what matters most is the ongoing ability to enter and exit fat-burning states, not continuous ketosis.
A note on this article: This post is for educational purposes and is not medical advice. Significant dietary changes, extended fasting, and carbohydrate restriction may not be appropriate for everyone and can interact with medications including insulin and blood sugar-lowering drugs. Please consult a qualified healthcare provider before making substantial changes to your diet or eating pattern.
Wondering where you sit metabolically?
If you've been experiencing energy crashes, carbohydrate cravings, difficulty losing weight despite doing "everything right," or you simply want to understand your metabolic health picture before it becomes a diagnosis this is exactly the kind of investigation a naturopathic assessment is built for. Book a free 15-minute discovery call and let's look at what your numbers are actually telling you.
About the author: Dr. Sonya Arrigo, ND is a Naturopathic Doctor practicing virtually across Ontario and in person at Insight Naturopathic Clinic in Toronto's Leaside neighbourhood. She holds an HBSc from the University of Toronto and a Doctor of Naturopathy from the Canadian College of Naturopathic Medicine, and is registered with the College of Naturopaths of Ontario.
