Keto Diet: Benefits, Risks and What the Evidence Says

The short version

• Keto limits carbs to about 20 to 50 grams a day, so your body uses fat and ketones for fuel.
• Early weight loss is often quick, but much of that is water, and long-term results aren't clearly better than other diets.
• Common downsides include "keto flu", constipation, rising LDL cholesterol in some people, and being hard to sustain.
• People on certain diabetes medications, or with some medical conditions, should only do it with medical supervision, if at all.

In a sentence

Very low carb and high fat, to keep your body in ketosis.

How restrictive

Counting needed?

Yes, carbs closely

Quality of evidence

Moderate

Typical cost

Higher

Main drawback

Hard to sustain, low in fiber, and LDL cholesterol can rise

See how this compares with every other diet →

How it works

When you cut carbs far enough, your body runs low on glucose and starts converting fat into molecules called ketones to use as fuel. That state is called ketosis. To stay there, a typical plan looks like this:

For scale, one medium banana has about 27 grams of carbs, so keto leaves little room for fruit, beans, grains or starchy vegetables.

What you eat

• Eat: Meat, fish, eggs, cheese, butter, olive oil, avocado, nuts, seeds, leafy and other low-carb vegetables
• Avoid: Bread, rice, pasta, cereal, sugar, most fruit, beans, potatoes and most alcohol

What the evidence says

Weight. Many people lose weight quickly on keto, helped by water loss and by the way ketosis seems to blunt appetite. Over a year or more, results tend to look similar to other diets, and few people stay on it.

Blood sugar. Keto can significantly lower blood sugar and reduce diabetes medication needs, under medical care. In the small Keto-Med crossover trial, though, a Mediterranean-style diet with fewer restrictions matched it on A1C and weight. LDL cholesterol rose about 10% on keto and fell on the Mediterranean-style diet, and people were less likely to stick with keto after the study ended.

Epilepsy. Keto is an established medical treatment for some forms of drug-resistant epilepsy. That was its original purpose, and it's done with specialist supervision.

Long-term safety. This hasn't been studied well. We don't have good evidence on what decades of keto does to the heart.

The first week: "keto flu"

As your body switches fuel, you may have headaches, fatigue, irritability, nausea, brain fog and muscle cramps. Part of this comes from losing water and electrolytes. It usually passes in about a week or so. Drinking plenty of water and getting enough salt can help, unless you've been told to limit sodium.

How to do it more safely

• Have your blood work done before starting and about three months in, especially cholesterol.
• Choose fish, olive oil, nuts and avocado over mostly bacon, butter and processed meats.
• Eat as many low-carb vegetables as you can, for fiber and nutrients.
• Treat it as a time-limited experiment and plan how you'll eat afterward. When you add carbs back, expect some water weight to return.

Other risks

• Constipation, from low fiber
• Kidney stones
• Nutrient shortfalls, including some vitamins and minerals
• Bad breath
• A more restrictive relationship with food

Is it worth trying?

If you have a lot of weight to lose or struggle with your blood sugar, like simple rules and don't mind the restrictions, keto is a legitimate option to try with medical support. If you love bread or fruit, or eat out a lot, a more moderate low-carb approach will get you much of the benefit with less hassle.

Sources

1. Harvard T.H. Chan School of Public Health: Diet Review: Ketogenic Diet
2. Gardner et al., Am J Clin Nutr (2022): Ketogenic vs Mediterranean-style diet (Keto-Med)
3. FDA-approved label for empagliflozin (Jardiance), an SGLT2 inhibitor: ketoacidosis warning

This guide is general information, not medical advice. Please check with a clinician before making big changes, especially if you have a health condition, take medication, or are pregnant. Read the full disclaimer.