Keto Diet
The ketogenic (keto) diet is a very low-carbohydrate, high-fat eating pattern that aims to shift the body into a metabolic state called ketosis, where fat becomes the primary fuel source. It has evolved from a medical treatment into a mainstream wellness trend, increasingly popular for it's promises of weight loss, stable energy and reduced cravings. Some applications have strong evidence; others do not. Understanding what keto does, and what it doesn't, is crucial before deciding whether it's right for you.
While some people feel better temporarily when reducing refined carbohydrates, keto is a highly restrictive approach and not suitable or necessary for most people.
The keto diet
A keto diet is a very low-carbohydrate, high-fat eating pattern designed to shift your body's primary fuel source from glucose (from carbohydrates) to ketones (from fat metabolism). Typically, keto involves
drastically restricting carbohydrates to fewer than 50 grams per day (and often 20–30g)
focusing meals around fats and moderate protein
limiting foods like grains, bread, pasta, most fruits and many vegetables
relying on high-fat foods such as oils, nuts, seeds, cheese, and some meats
When carbohydrate intake drops low enough, your body enters a metabolic state called ketosis, where the liver breaks down fat into ketone bodies, which the brain and body can use for energy. This shift is quite different from normal glucose-based metabolism.
The diet isn't new, it was originally used medically to manage epilepsy. More recently, it's been studied for weight loss, type 2 diabetes management, neurological health, and various other applications. It involves.
This way of eating is significantly different from balanced, long-term eating frameworks, and is often challenging to maintain.
What are the core principles of the keto diet?
Although versions vary across online sources, keto generally includes:
Very low carbohydrate intake, often under 50g per day (for comparison a standard diet includes 200-300g daily).
High fat intake, sometimes 60–80% of total energy and as such it becomes the primary energy source.
Moderate protein intake but not too highbecause excessive protein can interfere with ketone production (the body can convert excess protein to glucose)
Eliminating most grains, starchy vegetables and many fruits
Strict tracking which is often required to maintain ketosis
Avoiding hidden carbohydrates particularly in processed foods
It is a rule-heavy diet that relies on ongoing tracking and monitoring for most people.
Does the evidence support a keto diet?
The evidence for ketogenic diets is strongest in specific contexts, and more mixed in others.
Weight loss
Keto is effective for short-term weight loss, particularly in the first few months and has been shown to be comparable to, or slightly better than, low-fat diets. But after 12 months the difference between keto and other calorie-restricted diets becomes negligible. The weight loss appears to come from two factors: firstly, the restriction of carbohydrates naturally reduces food choice, which often leads to lower overall calorie intake. Secondly, the metabolic shift to fat burning may provide a modest advantage. But the 'magic' of ketones burning fat faster than other diets isn't strongly supported. What matters most is still energy balance.
Type 2 diabetes and blood sugar
Keto has shown promise for blood sugar control. People on very low-carbohydrate diets can rapidly improve fasting glucose and HbA1c levels in those with type 2 diabetes, sometimes within 1–2 weeks. However, this improvement often reflects the very low carbohydrate load, and similar benefits can be achieved with moderate carbohydrate restriction combined with whole grains and fibre rather than complete carb elimination. Additionally, long-term adherence to keto is challenging, and when people resume normal eating, improvements often reverse.
Cardiovascular effects
This is where the evidence becomes more concerning. While some studies show improvements in triglycerides and weight on keto, others show increases in LDL (i.e. 'bad' cholesterol), particularly if saturated fat intake is high. The long-term cardiovascular safety of very high saturated fat intake remains debated.
Neurological and mental health
Small studies have shown that keto may help stabilise severe mental illness, with participants showing improvements in psychiatric symptoms and metabolic health. Some people report improved mental clarity on keto; others report mood changes or brain fog. However more research is needed.
Athletic performance
Contrary to some claims, keto doesn't enhance athletic performance for most people. In fact, athletes often perform better with adequate carbohydrate availability. Keto may be useful for endurance athletes in specific contexts, but it's not optimal for high-intensity exercise or muscle building.
When would a keto diet be helpful?
Ketogenic eating might be worth exploring if you:
Have type 2 diabetes and want to explore blood sugar management through carbohydrate restriction. In this case working with your healthcare team is essential, as medication adjustments may be needed.
Are looking for rapid initial weight loss and can tolerate a very restrictive diet. The first few months typically show the most dramatic results but after this results are no different to other calorie controlled diets.
Have epilepsy because medically supervised ketogenic therapy remains an evidence-based treatment for certain seizure types, particularly in children.
Tolerate dairy well and enjoy high-fat foods. If your preferences naturally align with keto foods then adherence is easier.
These positive effects often stem from lower intake of refined carbohydrates, increased food awareness or reduced variety rather than ketosis itself.
When caution is needed
Several important cautions apply to ketogenic diets. Firstly it's very restrictive and hard to sustain long-term. Most people find keto difficult to maintain beyond 3–6 months. When carbohydrates are reintroduced, weight often returns, and blood sugar improvements may not persist without ongoing lifestyle changes. Alongside this:
There is an increased risk of nutrient deficiencies - the restriction of entire food groups increases the risk of inadequate fibre, certain vitamins (including thiamine and folate), and minerals. Supplementation is often necessary.
Keto flu - when starting keto, many people experience fatigue, headaches, and irritability for 1–4 weeks as the body adjusts. This can be severe enough that people abandon the diet.
Cardiovascular concerns - high saturated fat intake can raise LDL cholesterol in some people, which may increase cardiovascular risk long-term. Anyone with a family history of heart disease should monitor cholesterol carefully and consider a less extreme approach.
May worsen existing conditions - people with certain liver or kidney conditions, or those taking specific medications, should avoid keto without medical supervision.
Not suitable during pregnancy or breastfeeding - the restriction of nutrients and potential metabolic stress make keto inadvisable during these periods.
Hormonal effects - some women, experience disrupted menstrual cycles on very low-carb diets.
Expensive - maintaining keto on a budget is challenging, as animal products and specialty keto foods are costly.
For many people, more balanced carbohydrate adjustments feel gentler and more sustainable.
A Nutritional Therapists perspective
From a functional nutrition standpoint, keto has specific applications where it can be valuable. For someone with type 2 diabetes who wants to take control of blood sugar through diet, a ketogenic approach, ideally under professional guidance, can be transformative. The rapid improvements in glucose control are meaningful.
For weight loss specifically, keto works, but so do many other approaches. The best diet for weight loss is the one someone will actually stick with. If keto clicks for you and you can sustain it, the results can be significant. But for most people, a less extreme approach, like moderate carbohydrate reduction with whole grains and higher fibre, may be more sustainable and equally effective.
The concerning element is positioning keto as optimal for everyone. Your brain and muscles do function on ketones, but they also function very well on glucose from whole grains, legumes, and fruits. There's no evidence that ketosis is a metabolically superior state for the average person without diabetes or specific neurological conditions.
If you're considering keto, be honest about your tolerance for restriction and monitor how you feel. If energy, mood, and hormonal health dip, it may be worth exploring a less extreme approach to achieving your goals. More balanced approaches such as including slow-release carbohydrates, increasing fibre, building satisfying meals and supporting blood-sugar rhythm, often provide similar benefits without the need for strict rules.
Keto may offer short-term structure, but it rarely aligns with long-term wellbeing for most people.
I can help you
If you’re considering keto because you’re struggling with low energy, cravings or digestive symptoms, it can be useful to explore what’s really driving how you feel. Personalised nutrition can help you understand whether a restrictive approach is truly needed, or whether gentler, more sustainable changes would support you more effectively. Book a free call with me to discuss how appropriate keto is for you.
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