A keto diet can be especially useful for losing excess body fat without hunger and for improving type 2 diabetes.
Low-carb diets tend to be highly effective when it comes to weight loss:
The British Journal of Nutrition 2016: Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomized controlled trials [strong evidence]
A keto diet tends to reduce appetite:
Obesity Reviews 2014: Do ketogenic diets really suppress appetite? A systematic review and meta-analysis [strong evidence]
The advantage of a low-carb diet for improving type 2 diabetes is fairly clear:
Diabetes Research and Clinical Practice 2018: Effect of dietary carbohydrate restriction on glycemic control in adults with diabetes: A systematic review and meta-analysis [strong evidence]
1. What is a keto diet?
The keto diet is a very low-carb, higher-fat diet. It’s similar in many ways to other low-carb diets.
While you eat far fewer carbohydrates on a keto diet, you maintain moderate protein consumption and may increase your intake of fat. The reduction in carb intake puts your body in a metabolic state called ketosis, where fat, from your diet and from your body, is burned for energy.
What “keto” means
A “keto” or “ketogenic” diet is so named because it causes your body to produce small fuel molecules called “ketones.”
There are three different ketones, or “ketone bodies” used as fuel by the body. They are:
Learn far more than you’ll ever need about ketones here:
Dr. Peter Attia: Ketosis — advantaged or misunderstood state? (Part I)
This is an alternative fuel source for your body that can be used when blood sugar (glucose) is in short supply.
When you eat very few carbs or very few calories, your liver produces ketones from fat. These ketones then serve as a fuel source throughout the body, especially for the brain.
It’s a common misconception that all of the body only runs on ketones when on a keto diet. The truth is that most of the body — including the muscles — can burn fat directly. It would be a waste to have the liver first convert them into ketones.
The brain is a hungry organ that consumes lots of energy every day, and it can’t run on fat directly. It can only run on glucose — or ketones.
The brain consumes about 20% of the body’s required energy every day, despite only representing 2% of the body’s mass.
This could be a bonus for weight loss, if your hungry brain burns fat for you.
Another note: ketosis is why the old idea that “the brain needs carbohydrates” is wrong — the brain requires limited amounts of glucose even in ketosis, but the body can create that glucose from protein and fat in a process called gluconeogenesis.
Food for thought: Does the brain need carbs?
On a ketogenic diet, your entire body switches its fuel supply to run mostly on fat, burning fat 24–7. When insulin levels drop very low, fat burning can increase dramatically. It becomes easier to access your fat stores to burn them off.
In a large majority of high-quality trials, low-carb diets have been found to be more effective for weight loss than other diets:
PLOS ONE 2015: Dietary intervention for overweight and obese adults: comparison of low-carbohydrate and low-fat diets. A meta-analysis [strong evidence]
Low-carb diets might even increase metabolism — potentially increasing fat burning — by between 200 and 500 calories per day:
British Medical Journal 2018: Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial [moderate evidence] Analysis
As a side note, the increased fat burning can use either body fat, or dietary fat, or (usually) both. This means that eating more fat than you need to stay satisfied can slow down the burning of body fat stores. If you’re aiming to lose weight, only eat when you’re hungry. Learn more
This is great if you’re trying to lose weight, but there can also be other benefits, such as less hunger and a steady supply of energy — without the sugar peaks and valleys that often occur when eating high-carb meals. This may help keep you alert and focused.
This is something that is often reported by people on a keto diet [very weak evidence]. According to our expert panel, this happens in approximately 70% of the patients they treat with keto diets.
The scientific support isn’t very strong. Here are references showing minor signs of improvements:
European Journal of Clinical Nutrition 2013: Ketosis and appetite-mediating nutrients and hormones after weight loss[randomized trial; moderate evidence]
Neurobiology of Aging 2012: Dietary ketosis enhances memory in mild cognitive impairment[moderate evidence for verbal memory improvement in people with early Alzheimer’s]
Epilepsy Research 2012: The effects of the ketogenic diet on behavior and cognition[overview article; ungraded]
Journal of the Association of Nurses for AIDS Care 2019: Cognitive effects of a ketogenic diet on neurocognitive impairment in adults aging with HIV: a pilot study [randomized trial; moderate evidence]
When the body produces ketones, it enters a metabolic state called ketosis. The fastest way to get there is by fasting — not eating anything — but nobody can consistently fast forever.
The ketosis experienced after a longer period of fasting is called starvation ketosis. But since starvation is neither healthy nor sustainable, we focus more on nutritional ketosis. However, intermittent fasting may have a role as an adjunct to diet for health gains and weight loss. Read more in our guides on intermittent fasting and time restricted eating.”
A keto diet, on the other hand, also results in ketosis and can be eaten indefinitely. It has many of the benefits of fasting — including weight loss — without having to fast long term.
Who should NOT do a ketogenic diet?
There are controversies and myths about a keto diet, but for most people it appears to be very safe.
The main fear about lower-carb and higher-fat diets has always been an increase in the risk of heart disease. However, interventional studies so far indicate that if anything the risk appears to decrease:
- British Journal of Nutrition 2016: Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomized controlled trials. [strong evidence for improved risk factors]
- PLOS ONE 2015: Dietary intervention for overweight and obese adults: comparison of low-carbohydrate and low-fat diets. A meta-analysis. [strong evidence for improved risk factors]
- Obesity reviews 2012: Systematic review and meta‐analysis of clinical trials of the effects of low carbohydrate diets on cardiovascular risk factors [strong evidence for improved risk factors]
- Circulation 2010: Dietary intervention to reverse carotid atherosclerosis [moderate evidence for a reduction in atherosclerosis]
However, three groups often require special consideration:
- Do you take medication for diabetes, such as insulin?
- Do you take medication for high blood pressure?
- Do you breastfeed?
2. What to eat on a keto diet
Here are typical foods to enjoy on a ketogenic diet. The numbers are net carbs per 100 grams (3.5 ounces) of food.
Net carbs (or “digestible carbs”) are total carbs minus fiber. Fiber generally doesn’t directly affect blood sugar levels.
Learn more about carbs and net carbs on a keto diet
To remain in ketosis, lower is generally better:
What’s the most important thing to do to reach ketosis? Avoid eating too many carbs. You’ll likely need to keep carb intake under 50 grams of net carbs per day, ideally below 20 grams.
Subtracting fiber from total carbs to calculate net carbs is useful for natural foods, such as vegetables, fruits and nuts. However, it may be less helpful for processed or packaged foods.
Since we recommend eating mostly natural, minimally processed foods, we focus on net carbs. However, if you find yourself eating low-carb packaged foods, then we suggest using total carbs rather than net carbs as your guide.
The fewer the carbs, the more effective the diet appears to be for reaching ketosis, losing weight or improving type 2 diabetes.
This is mainly based on the consistent experience of experienced practitioners, and stories from people trying different levels of carb restriction [weak evidence].
One trial showed that diets providing 20 grams and 50 grams of carbs equally helped healthy volunteers maintain ketosis. However, we don’t know if the same is true for people with obesity, insulin resistance or diabetes.
In addition, there is not yet an RCT that tests the health benefits of two low-carb diets of varying strictness head-to-head. But RCTs of strict low-carb diets appear to show better results compared to RCTs of more moderate or liberal low-carb diets:
Obesity Reviews 2016: Impact of low‐carbohydrate diet on body composition: meta‐analysis of randomized controlled studies [strong evidence for fat mass loss on very low-carb diets in particular]
You can read even more studies in our Science of low carb and keto guide:
RCTs of low-carb interventions for weight loss
Counting carbs can be helpful at first. But if you stick to our recommended foods and recipes you can stay keto even without counting.
Try to avoid
Here’s what you should avoid on a keto diet — foods containing a lot of carbs, both the sugary and the starchy kind. This includes starchy foods like bread, pasta, rice and potatoes. These foods are very high in carbs.
The numbers are grams of net carbs per 100 grams (3.5 ounces), unless otherwise noted.
Net carbs (or “digestible carbs”) are total carbs minus fiber. Fiber generally doesn’t affect blood sugar levels.”
Also avoid or limit highly processed foods and instead follow our whole foods keto diet advice.
You should also avoid low-fat diet products. A keto diet should be moderately high in protein and will probably be higher in fat, since fat provides the energy you’re no longer getting from carbohydrate. Low-fat products usually provide too many carbs and not enough protein and fat.
What to drink
What can you drink on a ketogenic diet? Water is the perfect drink, and coffee or tea are fine too. Ideally, use no sweeteners, especially sugar.
Even zero-calorie sweeteners may have negative effects in some people, including maintaining a preference for sweet tastes and potentially increasing the risk of overeating and even food addiction. This is mainly based on clinical experience [weak evidence].
There is also one RCT study showing weight loss from avoiding artificial sweeteners:
The American Journal of Clinical Nutrition 2015: Effects on weight loss in adults of replacing diet beverages with water during a hypo-energetic diet: a randomized, 24-wk clinical trial [moderate evidence]
For more, check out our guide to keto sweeteners or have a look at these further references:
International Journal of Obesity 2017: Effects of aspartame-, monk fruit-, stevia- and sucrose-sweetened beverages on postprandial glucose, insulin and energy intake [randomized crossover trial; moderate evidence]
Physiology & Behavior 2016: Recent studies of the effects of sugars on brain systems involved in energy balance and reward: relevance to low calorie sweeteners [animal data; very weak evidence]
PLOS Medicine 2017: Artificially sweetened beverages and the response to the global obesity crisis [overview article; ungraded]
A splash of milk or cream in your coffee or tea is OK, but beware that the carbs can add up if you drink multiple cups in a day (and definitely avoid caffe lattes!). The occasional glass of wine is fine too.