Specific diets

Intermittent fasting, keto, vegan, Mediterranean… what the evidence says about each approach and which one suits you.

How to compare diets rigorously

Almost all diets share the same underlying mechanism: they make you eat fewer calories, whether by eliminating food groups, restricting timing or increasing satiety. When a study matches calories and protein between two diets, the differences in fat loss usually disappear. The most common mistake when reading about diets is attributing to a special rule (no gluten, no carbs at night…) what is really just eating less.

How to apply it

• Before believing a diet 'works through its special mechanism', ask yourself whether it simply made you eat less
• Judge any new diet first by whether it controls calories and protein, not by its narrative

Adherence matters more than the type of diet

Large comparative trials (A TO Z: Atkins vs. Zone vs. LEARN vs. Ornish; DIETFITS: low-carb vs. low-fat, ~600 people, 12 months) find no clear winner among diet types for weight loss. The variability within each group is enormous: on the same protocol, some people lose a lot and others gain weight. The real predictor is not the diet but how faithfully and for how long it is followed.

How to apply it

• Choose the diet you can sustain alongside your life and your tastes, not the one promising the fastest results
• The goal is not the diet that 'works' for 8 weeks: it is the one you can keep up for years

Flexible dieting (IIFYM): the default approach

'If It Fits Your Macros' sets calorie and macro targets (especially protein) without banning any food. It reduces the feeling of deprivation and the risk of binges compared with more rigid diets, and along the way it teaches portion sizes that are useful for future maintenance. Its weakness is that 'flexible' misunderstood can turn into eating only processed foods that fit your macros while neglecting fibre and micronutrients: hence a simple rule of 80–90% minimally processed foods.

How to apply it

• If you struggle with rigid rules, try setting only calories and protein and leaving the rest flexible
• Apply the 80/20 rule: most of your food from minimally processed sources, a small margin at your discretion

Intermittent fasting: what it promises and what it delivers

When calories and protein are matched, intermittent fasting (16:8, 5:2, alternate-day fasting) does not produce more fat loss than an equivalent continuous diet: there is no 'fat-burning mode' exclusive to fasting. Its real value is as an adherence tool: for many people, restricting when they eat spontaneously lowers how much they eat, without having to count anything. It is not recommended in eating disorders, pregnancy, or for anyone who needs regular intake because of medication.

How to apply it

• Try intermittent fasting only if it suits you, not because you think it 'burns more fat'
• If you train strength seriously, check that your eating window lets you fit in enough protein, spread out

Low-carb and keto: the initial weight loss is mostly water

Restricting carbohydrates depletes glycogen, which holds ~3 g of water per gram: that explains the 2–4 kg lost in the first few days, which is not fat and comes back when you reintroduce carbs. At equal calories and protein, keto does not lose more fat than other diets, although some people find it very satiating and it helps them eat less without counting. Its best real evidence is in glycaemic control in type 2 diabetes, not in body composition.

How to apply it

• Do not confuse the rapid drop in the first days of keto with fat loss: it is water
• If you do high-intensity efforts (sprints, heavy lifting), severe carbohydrate restriction tends to harm performance

Low-fat diets: as valid as low-carb, given a bad name by the 90s

At equal calories and protein, a low-fat diet loses as much body fat as a low-carb one: neither has a real metabolic advantage. Its bad reputation comes from the ultra-processed 'light' products of the 90s (fat-free biscuits loaded with sugar); the version with real evidence is built on whole foods (pulses, whole grains, vegetables, fruit) with enough fat for hormones and vitamins (a minimum of ~0.5–0.8 g/kg).

How to apply it

• If food volume fills you up more than fat does, a lower-fat diet higher in quality carbohydrate may suit you better than keto
• Do not drop fat below 0.5 g/kg even on a low-fat approach

Carb cycling and refeeds: fine-tuning, not essential

Alternating high and low carb days (aligning the high ones with your hard sessions) or adding periodic 'refeeds' within a deficit has little demonstrated advantage over a linear isocaloric diet for body composition: what rules is still your weekly balance. Where they do help is with adherence and psychological relief during long deficits, and perhaps in somewhat mitigating metabolic adaptation.

How to apply it

• Consider a refeed or a diet break (1–2 weeks at maintenance) if you have spent many weeks in a deficit and feel mentally fatigued
• Do not complicate your diet with cycling if you have not nailed the basics yet (consistent calories and protein): it is last-level optimisation

The Mediterranean diet: the best long-term health evidence

More than a macro protocol, it is a pattern: plenty of vegetables, fruit, pulses, nuts and whole grains, olive oil as the main fat, fish often, red meat occasionally. The PREDIMED trial and numerous cohorts associate it with lower cardiovascular risk, less type 2 diabetes and lower mortality. It is not the most direct tool for losing fat fast, but its high satiety makes a spontaneous deficit easier and it is excellent as a base for long-term maintenance.

How to apply it

• If you want a healthy, lifelong sustainable starting point, the Mediterranean pattern is among the best supported there is
• You can layer other strategies (fasting, flexible dieting) on top of a Mediterranean-style food base

Plant-based diets: how to do it well

Well planned, vegetarian and vegan diets are adequate at any stage of life and are associated with cardiometabolic benefits. To build muscle on a vegan diet, push protein towards the high end (~1.6–2.2 g/kg), combine pulses with grains to cover the essential amino acids, and lean on plant protein powder if needed. Vitamin B12 requires mandatory supplementation on a strict vegan diet; also keep an eye on iron, omega-3, calcium, vitamin D, zinc and iodine.

How to apply it

• If you are vegan and train strength, raise your protein target and combine different plant sources across the day
• Supplement B12 without exception if you are strictly vegan; review iron and omega-3 with your doctor

High protein vs. the carnivore diet: one is supported, the other is not

Raising your protein (often >2 g/kg) is, of all the possible dietary adjustments, the one with the best support for improving body composition: it protects muscle in a deficit, is more satiating and does not harm the kidneys or liver in healthy people, even at sustained high doses. The carnivore diet (animal products only) is the opposite extreme: with no quality trials to support it, its supposed benefits are better explained by cutting out processed food and eating in a deficit, and it carries real risks from the total absence of fibre and certain micronutrients.

How to apply it

• If you are only going to change one thing about your diet, make it raising your protein: it is the lever with the best effort-to-result ratio
• Be suspicious of diets that eliminate whole food groups without a clear medical reason, such as carnivore

How to spot a fad diet

Be suspicious if it promises fast, extraordinary results, if it demonises a single food or macronutrient as the cause of everything, if it talks about 'toxins' or 'detox' without specifying which (your liver and kidneys already do that job), if it depends on buying the brand's own products, if it leans on testimonials and before/after photos instead of trials, or if it eliminates entire food groups without clinical justification.

How to apply it

• If a diet ticks several of these warning signs at once, it is more marketing than science
• Always ask yourself: does this reduce ultra-processed food and raise satiety, or does it promise something beyond that?