Keto Diet: A Beginner’s Guide

What is the keto diet?

“Keto” is short for ketogenic diet: a very low-carbohydrate, high-fat way of eating with a moderate amount of protein.^[1][3] It isn’t new. Doctors have used carefully managed ketogenic diets for about a century, most notably to help children with epilepsy that doesn’t respond to medication.^[1][2] Its popularity as a weight-loss approach is much more recent.

Carbohydrates are usually the body’s main source of quick energy. When very little carbohydrate is eaten, the liver steps up production of ketones, made from fat, as an alternative fuel.^[1][3] That fat can come from food you eat as well as from the body’s fat stores, so being in ketosis doesn’t mean all the fat being used is stored body fat.^[3]

The body doesn’t stop using glucose altogether. At first it draws on stored glucose, and it can also make some glucose from protein, which is one reason keto plans keep protein moderate rather than high.^[1] Mild ketosis also happens naturally, for example overnight while you sleep.^[1]

There is no single standard keto diet, and food lists from different sources vary and sometimes conflict.^[1] Keto is one eating pattern among many. It isn’t required for weight loss, and it isn’t the right choice for everyone.

How does ketosis work?

In simple terms, ketosis is the body adjusting to a much lower supply of carbohydrate. This is a general explanation of the process, not instructions for getting into ketosis.

1. 1

   Step 1: Carbohydrate intake drops substantially

   With very little carbohydrate coming in, the body first uses its stored glucose. How quickly those stores run down varies from person to person.^[1][3]

2. 2

   Step 2: The liver makes more ketones

   As insulin levels fall, the liver increases its production of ketones from fat. When ketones build up in the blood, this is called ketosis.^[1][3]

3. 3

   Step 3: Ketones are used alongside other fuels

   Many cells, including the brain, can use ketones for energy. The body still uses glucose too, including glucose it makes from protein.^[1][2]

How long this takes and how many ketones build up differs between people, depending on things like body composition and metabolism.^[1][3]

Foods commonly included and limited

Keto plans differ, but most follow a similar pattern. These lists describe what keto plans usually include or limit. They don’t say whether a food is healthy or unhealthy.^[1][3]

Preparation and amounts matter. Fruit, beans, lentils and whole grains are limited on keto because of their carbohydrate content, not because they are harmful. Outside keto, they are good sources of fiber, vitamins and minerals.^[1]

Fat sources vary a lot between keto plans. Some lean heavily on butter, fatty and processed meats. Others emphasize olive oil, avocado, nuts, seeds and oily fish, which are lower in saturated fat.^[1][2] If you’d like to see how a typical meal is built more broadly, read how to build a balanced plate.

Keto and weight loss: what to understand

Weight loss is the main reason many people try keto. Here is what the evidence does and doesn’t show.

• Some people lose weight on keto

  Studies show keto can lead to weight loss in the short term, along with improvements in some health markers.^[1] Proposed reasons include feeling fuller and having fewer cravings, though these explanations haven’t been consistently shown.^[1]

• Early changes can include water

  Short-term changes on the scale are often driven by water. Meals high in carbohydrates can make the body hold extra water for a while, so a sharp cut in carbohydrates can change the scale quickly without all of it being body fat.^[4] See water weight vs. fat loss.

• Ketosis doesn’t guarantee fat loss

  Ketones can be made from fat you eat as well as from stored body fat, so being in ketosis doesn’t by itself mean you are losing body fat.^[3]

• Long-term results aren’t clearly better

  Keto sometimes produces faster weight loss at first than other diets, but that difference tends to disappear over time.^[2] After about a year, results haven’t been significantly different from conventional weight-loss diets, and much of the research is small and short-term.^[1]

• What you can keep up matters most

  Because keto removes several food groups, many people find it hard to stick with.^[1][2] Your health, preferences, budget and daily life all affect which approach you can realistically maintain.^[7]

Considerations before trying keto

Keto can work for some people, but it has real trade-offs. This is general information, not a personal assessment.

Frequently asked questions