Keto: stop eating carbs and your body burns fat. Mostly true.
The most hyped diet of the last ten years actually works, just not the way the influencers sell it. Here is what it does, what the science says, and who should stay well away from it.
The short version
- What it is
- Carbs down to about 20–50 g a day, fat way up, protein moderate.
- Good for
- Killing hunger, steady blood sugar, epilepsy that drugs can't control.
- Bad at
- Lasting forever. Also bad for your cholesterol in some people.
- Evidence
- Moderate. Strong for epilepsy.
- Our take
- Brilliant tool, lousy religion. We use it for the meal that breaks your fast.
What keto actually is
Your body runs on sugar by default. Bread, rice, pasta, potatoes, fruit juice, all of it ends up as glucose in your blood. Keto takes that away. You cut carbohydrates so low, usually under 50 grams a day (one large banana is already around 30), that your body is forced to switch fuel.
It then burns fat, and your liver turns part of that fat into ketones, a backup fuel your brain can run on. That state is called ketosis. That's the whole trick. Everything else is marketing.
The medical version used for epilepsy is much stricter: four parts fat to one part protein and carbs combined.1 The keto you see on Instagram is the relaxed cousin.
How it works in your body
Your body keeps a small sugar reserve called glycogen in the liver and muscles. Stop eating carbs and that reserve runs dry within a day or two. Each gram of glycogen is stored with water, so when it goes, the water goes too. That's why the scale drops so fast in week one. It's water, not fat. Sorry.
After two to four days of very low carbs, ketone levels climb and most people are in ketosis. From then on, the main draw is appetite: ketones seem to dampen hunger. That's where keto earns its reputation.
What you eat, what you don't
Eat
- Eggs, fish, sardines, salmon, meat
- Olive oil, avocado, butter, cheese
- Nuts and seeds
- Leafy greens, broccoli, cauliflower, zucchini, peppers
- Berries, in small amounts
- Water, black coffee, green tea
Forget it
- Sugar in every form, soft drinks, juice
- Bread, rice, pasta, noodles
- Potatoes and most root vegetables
- Most fruit, including bananas and mango
- Beer
- Beans and lentils (yes, the healthy ones too)
Alcohol on keto
OK, now and then
- Vodka, gin, whisky, tequila, rum, Obstler: neat, on ice or with soda water and lime (0 g carbs)
- One glass of dry red or white wine (about 4 g)
- A G'spritzter: dry wine topped up with soda water
- Sparkling wine labelled brut nature or extra brut
Kicks you out of ketosis
- Beer (about 12 g a bottle), cider
- Cocktails, liqueurs, sweet wine
- Anything mixed with juice, cola, tonic or energy drinks
- "Diet" or "zero" mixers: sweeteners are on our never list
50 Club: one light beer (about 5 g) or a small sake.
Zero carbs doesn't mean zero effect. While your liver deals with alcohol, it puts fat burning on hold: two drinks cut fat burning by about 73% in one study.7 Never drink while fasting or on an empty stomach. All the details are in our alcohol guide.
What it's good for, with proof
You stop being hungry all the time
Normally, when you eat less, hunger fights back hard. A meta-analysis from the University of Sydney found that people on ketogenic diets were slightly less hungry and had less desire to eat, even while losing weight.3 The real win isn't that keto makes you full. It's that it stops hunger from getting worse while you lose weight. For anyone who's fat and constantly starving on a "normal" diet, that's a big deal.
Weight loss, a little more than low-fat
Thirteen randomised trials, about 1,400 people, followed for a year or more: the keto groups lost more weight than the low-fat groups.2 By how much? Under a kilo. So keto works, but it isn't magic. It works because you eat less, and it makes eating less easier.
Calm blood sugar
In a tightly controlled US government study, people's blood sugar and insulin stayed lower and steadier on keto than on a high-carb diet.4 No spikes, no crash, no 3 pm attack on the biscuit tin.
Epilepsy, where it's real medicine
This is keto's original job, going back about a hundred years. In children whose epilepsy doesn't respond to drugs, a ketogenic diet clearly cuts seizures. In the Cochrane review, roughly one in three treated children got a meaningful reduction.1 That's done with a specialist team, not with a cookbook.
The uncomfortable truth
"Carbs make you fat, fat doesn't." Not that simple. In the same controlled study, the same people ate around 700 calories a day more on keto than on a low-fat, plant-based diet, and lost less body fat.4 Fat is calorie-dense. Pile bacon and cheese on everything and keto stops working.
Keto isn't a licence to eat unlimited fat. It's a way to cut the stuff that makes you hungry. Eat real food and stop when you're full.
The risks
- Keto flu. Headache, tiredness, brain fog, cramps in the first week as your body switches fuel and dumps water and salt. Usually gone in a few days. Drink water, salt your food. Unless you have high blood pressure, heart or kidney disease: then talk to your doctor first.
- Cholesterol. In the long-term trials, LDL ("bad") cholesterol went up on keto compared with low-fat.2 In some people it shoots up a lot. Get a blood test before and a few months after.
- Constipation. No bread, no beans, little fruit means little fibre. Eat your vegetables, a lot of them.
- Kidney stones. Seen in long-term medical keto, mainly in epilepsy patients. If you've had stones before, talk to your doctor first.
- Diabetes drugs. This one is serious. Keto combined with SGLT2 diabetes drugs (empagliflozin/Jardiance, dapagliflozin/Forxiga, canagliflozin/Invokana) can trigger a dangerous acid build-up in the blood, even with normal sugar levels.5 On insulin or similar medication, your doses may need changing. Never do keto on these drugs without your doctor.
- It's hard to keep up. Birthday cake, rice at every hawker centre, Schnitzel with Erdäpfelsalat. Most people quit. A diet you quit doesn't work.
Allergies: watch the staples
Keto leans hard on foods that are major allergens. If you're allergic, the plan has to swap them out, not just drop them.
| Keto staple | Allergen (EU list of 14)6 | Swap |
|---|---|---|
| Eggs | Eggs | Tofu scramble, fish, avocado |
| Cheese, butter, cream | Milk | Olive oil, coconut cream, avocado |
| Almonds, walnuts, almond flour | Tree nuts | Pumpkin and sunflower seeds |
| Peanut butter | Peanuts | Sunflower seed butter |
| Salmon, sardines, tuna | Fish | Eggs, meat, flax and chia for omega-3 |
| Prawns, crab, mussels | Crustaceans, molluscs | Fish, chicken |
| Tofu, tempeh | Soy | Eggs, fish |
| Keto mayonnaise, dressings | Eggs, mustard | Olive oil and lemon |
Don't do keto if you…
- are pregnant or breastfeeding
- have type 1 diabetes, or take insulin or SGLT2 drugs
- have kidney, liver or pancreas disease, or had your gallbladder removed
- have ever had an eating disorder
- are under 18
Healthen me asks about all of these and gives you a different plan if any apply.
How we use keto in your plan
We don't put you on keto for life. We use the best part of it.
You fast as long as you comfortably can. When you break the fast, your first meal is keto-friendly: eggs, sardines, avocado, olive oil, greens. Your blood sugar stays calm, hunger stays down, and you keep the benefits of the fast going longer.
After that, your meals are low-carb with real food. Rice and potatoes aren't banned. They're just not the best choice, and you'll know why.
This article is general information, not medical advice. If you have a medical condition or take medication, talk to your doctor before changing how you eat.
Sources
- Martin-McGill KJ et al. Ketogenic diets for drug-resistant epilepsy. Cochrane Database of Systematic Reviews 2020. doi.org/10.1002/14651858.CD001903.pub5
- Bueno NB et al. Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials. British Journal of Nutrition 2013;110(7):1178–1187. pubmed.ncbi.nlm.nih.gov/23651522
- Gibson AA et al. Do ketogenic diets really suppress appetite? A systematic review and meta-analysis. Obesity Reviews 2015;16(1):64–76. pubmed.ncbi.nlm.nih.gov/25402637
- Hall KD et al. Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake. Nature Medicine 2021;27:344–353. doi.org/10.1038/s41591-020-01209-1
- US Food and Drug Administration. Drug Safety Communication: SGLT2 inhibitors for diabetes may result in a serious condition of too much acid in the blood, May 2015; and Mistry S, Cocks Eschler D. Euglycemic diabetic ketoacidosis caused by SGLT2 inhibitors and a ketogenic diet. AACE Clinical Case Reports 2021. pmc.ncbi.nlm.nih.gov/articles/PMC7924151
- Regulation (EU) No 1169/2011 on food information to consumers, Annex II (the 14 allergens). eur-lex.europa.eu/eli/reg/2011/1169/oj
- Siler SQ, Neese RA, Hellerstein MK. De novo lipogenesis, lipid kinetics, and whole-body lipid balances in humans after acute alcohol consumption. American Journal of Clinical Nutrition 1999;70(5):928–936. pubmed.ncbi.nlm.nih.gov/10539756