What is a keto diet, and other common questions
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Frequently asked questions
Click on any question for the answer, or scroll down below for all of them.
- What is a keto diet?
- What is ketosis?
- Is a keto diet safe?
- How do you know when your body is in ketosis?
- What foods can you eat on a keto diet?
- Is a keto diet safe for the kidneys?
- Is ketosis safe for diabetics?
- What can you drink on the keto diet?
- How many carbs can you eat and still be in ketosis?
- Is a keto diet safe for high cholesterol?
- Can you be in ketosis and still not lose weight?
- How long does it take to be in ketosis?
- Can I have fruit on a keto diet?
- How long can someone be on a keto diet?
- Can I eat a keto diet as a vegetarian or vegan?
- What should my ketone level be in ketosis?
- What can I do for keto breath?
- Can I have dairy on keto?
- Can you build muscles on keto?
- What’s the difference between low carb and keto?
- Why am I not in ketosis?
- Should you aim for high ketone levels to speed up weight loss?
- At what time of the day should you test ketone levels?
- Is keto safe during pregnancy?
What is a keto diet?
A keto diet is a low-carb diet that results in ketosis. To achieve this, the diet has to be very low in carbohydrates, and no more than moderate in protein.
Usually the diet is also high in dietary fat, at least long term. In a more short-term diet, this is not always necessary. It’s possible to instead be fueled via your own fat stores, as long as you have excess weight to lose.
What is ketosis?
Ketosis is a normal process allowing your body to keep working when you eat few carbohydrates.
Carbs are one of two major fuels for the body. We can also burn fat for energy, but the brain can’t burn fat directly. Instead, when eating very low carb, fat is converted in the liver to ketones that are released into the blood stream. This is a great fuel for your brain.
The process of fueling the entire body with fat, including the production of ketones, is called ketosis. Under normal circumstances ketosis is safe and natural, for example when it is the result of a low-carb (“keto”) diet, or while fasting.
However, under certain special circumstances – most commonly with type 1 diabetes – ketosis can be a sign of insulin deficiency, and the ketones can then rise to potentially harmful levels.
Is a keto diet safe?
A keto diet is usually very safe. However, in the following three situations you may need extra preparation or adaptation:
- Are you on medication for diabetes, e.g. insulin? Learn more
- Are you on medication for high blood pressure? Learn more
- Are you breastfeeding? Learn more
If you’re not in one of these situations, you’ll likely do fine on a keto diet, without needing any special modifications.
Note that there’s no shortage of myths and misunderstandings about keto, that frighten children and grownups alike. So if you’re worrying about something in particular, check out this link.
How do you know when your body is in ketosis?
Any of these signs may indicate you are in ketosis:
- Decreased appetite and increased energy levels.
- Increased thirst and urination.1
- “Keto breath”, which may be more apparent to others than to yourself. Learn more
- Dry mouth or a metallic taste in your mouth.
Beyond these signs and symptoms, you can measure your level of ketosis, using one of three methods:
Learn more here: How to know you’re in ketosis
What foods can you eat on a keto diet?
Eat real low-carb foods like meat, fish, eggs, vegetables and natural fats (like olive oil or butter). A simple rule for beginners is to eat foods with fewer than 5% carbs (numbers above2).
Is a keto diet safe for the kidneys?
Yes. People often wonder about this, because of the belief that a diet high in protein could be harmful for the kidneys. However, this fear is simply based on two misunderstandings:
- A keto diet is high in fat, not protein.
- People with normal kidney function handle excessive protein just fine.3
Thus, there’s no reason to worry. In fact, a keto diet may even be protective of your kidneys, especially if you have diabetes. Learn more
Is ketosis safe for diabetics?
A keto diet leading to ketosis is generally a very powerful treatment to reverse type 2 diabetes.
People with type 1 diabetes can use a keto or low-carb diet to significantly improve their blood-sugar control. They will however normally always require insulin injections, but usually far lower doses on keto. They need to take care to not take too low doses and end up with ketoacidosis, or too high and end up with hypoglycemia.
Both people with type 1 and type 2 may rapidly require a reduction in medication on a keto diet to avoid hypoglycemia.
What can you drink on the keto diet?
The quick answer: Water is perfect and zero carb, as are coffee and tea (without sugar, of course). The occasional glass of wine is fine too.
How many carbs can you eat and still be in ketosis?
This varies, but generally it’s a good idea to stay below 20 net carbs per day.
Is a ketogenic diet safe for high cholesterol?
Generally, the cholesterol profile tends to improve on a keto diet, lowering triglycerides and raising the good HDL cholesterol.
However, a small minority of people may end up with quite high total cholesterol. Whether this is dangerous or safe is debated – there are no quality studies to determine the answer. But should you be one of the few where cholesterol may get up very high, e.g. over 400, you may want to take steps to reduce it just to be safe.
Can you be in ketosis and still not lose weight?
Yes. If so, check out our guide to weight loss.
How long does it take to be in ketosis?
It varies, from a day or two, up to a week or more. People with more insulin resistance (e.g. people with type 2 diabetes) usually take longer, while young and lean people generally get into ketosis far more quickly.
Can I have fruit on a keto diet?
However, certain berries are an exception that can be enjoyed in small amounts. The best choices are blackberries, raspberries, and strawberries, which provide 5-6 grams of carb per 100 grams (3½ ounces).
Most other fruits – including blueberries – contain double or triple this amount of carbs, as reflected in this guide to the best and worst fruits in terms of carb content.
Keep in mind that berries don’t provide any nutrients that can’t be found in vegetables and other foods with fewer carbs, so they are entirely optional on a keto diet. In fact, if you are very insulin resistant, you might be better off not having them.
How long can someone be on a keto diet?
Can I eat a keto diet as a vegetarian or vegan?
A keto diet can work for many non-meat-eaters, depending on what other types of food their diets include.
A lacto-ovo vegetarian eats dairy and eggs, whereas a lacto-vegetarian eats dairy but doesn’t eat eggs. There is also a subset of vegetarians known as pescatarians who include fish in their diet but avoid poultry and other meat.
Although following keto as a vegetarian is definitely doable, it can be a little challenging, especially when first starting out.
Our keto vegetarian meal plan provides several well-balanced, healthy meat-free meals.
On the other hand, a ketogenic vegan diet isn’t a well-balanced or sustainable option. Because vegans exclude all animal products, they must rely on a combination of grains, legumes, and seeds to get all the essential amino acids their bodies need. For this reason, a keto diet and vegan diet don’t work well together. Therefore, you’ll need to make a choice between the two or consider following a keto vegetarian diet, as described above.
What should my ketone level be in ketosis?
Generally above 0.5 mmol/l. Learn more
What can I do for keto breath?
Can I have dairy on keto?
Dairy is nutritious that can be part of a keto diet in many cases. However, whether you personally should eat dairy may depend on your health goals, along with your personal response to it.
For instance, although a higher dairy intake has been linked to fat loss and reduced diabetes risk in several studies, it has also been found to raise insulin levels. Indeed, some people find that cutting back on dairy helps with weight loss.
It’s also important to avoid high-carb options typically considered “healthy,” such as nonfat milk and nonfat yogurt. Instead, focus on these high-fat choices, preferably from naturally raised animals:
- Sour cream
- Cream cheese
- Plain whole-milk yogurt, Greek yogurt, or kefir
Can you build muscle on keto?
What’s the difference between low-carb and keto diets?
Keto is a very strict low-carb diet, that also puts even more emphasis on moderating the protein intake, and relying primarily on fat to supply energy needs.
A regular strict low-carb diet will likely put most people in ketosis anyway. But a keto diet tweaks things even further to make sure it’s working and, if desired, to get even deeper into ketosis.
Why am I not in ketosis?
The two most common reasons for not getting into ketosis are:
- Too many carbs
- Too much protein
For more tips see our full guide above. Please note that the amounts that people tolerate while staying in ketosis are individual, differing from person to person. Here’s the first of a 3-part series of blog posts about how our coworker Bjarte Bakke found out how to get into optimal ketosis: Why you’re not in ketosis
Should you aim for high ketone levels to speed up weight loss?
Yes and no. Eating fewer carbs, less protein and doing intermittent fasting certainly promotes weight loss, while lowering insulin and raising ketones.
However, adding extra fat to raise ketone levels does not promote weight loss. Neither does supplementing with MCT oil to raise ketone levels, or drinking “exogenous” ketone supplements. These methods actually slow down weight loss, by providing alternative fuel to be used instead of burning body fat.
If you want to lose weight, only use these methods – MCT oil or exogenous ketones – when you are hungry, or for performance reasons (unrelated to weight loss). Learn more
At what time of the day should you test ketone levels?
For comparison purposes, it’s good to measure about the same time every day. Measuring in the morning before eating makes it easier to compare the result from day to day.
However, morning numbers are usually among the lowest of the day, while evening numbers are higher. So if for some reason you want impressively high numbers, measure in the evenings instead. Be aware that your ketone levels don’t distinguish between the burning of dietary fat and stored fat.
Is keto safe during pregnancy?
A keto diet appears to be safe during pregnancy, judging from the experiences of people who have done it and doctors used to treating patients using a keto diet during pregnancy. It may also be very helpful in case of gestational diabetes.
However, there are no scientific studies on the subject, so there is a lack of definite knowledge. Possibly it’s wise to exercise caution and aim for a more moderate low-carb diet during pregnancy, unless there are important health benefits of doing a keto diet in your specific case. Learn more
More low-carb Q&A
Carb restriction and ketosis leads to an increase in excretion of fluids and reduced swelling in the body. ↩
The numbers are net carbs, i.e. grams of digestible carbs per 100 grams. ↩
Here’s an overview of scientific studies on this topic:
Note that people with dramatically reduced kidney function, i.e. people close to needing dialysis, may get instructions from their doctor to reduce protein intake. This advice should of course be followed. However, note that it does not stop that person from doing a keto diet, as the diet is not high in protein in the first place. ↩