What does “keto” mean, and what’s the diet like?
“Keto” is short for ketogenesis, which is the production and build-up of ketones. Ketones are a byproduct of fat metabolism, and they increase when carbohydrates are restricted, and the body is forced to rely more heavily on fat as a substrate for energy.
In considering whether to follow a diet that intentionally alters normal metabolism, it is helpful to have some understanding of how the body — and the keto diet — is designed to work.
At rest, our bodies typically burn a fairly even mix of fat and carbohydrates. Protein plays other important roles but is not typically included in the regular energy mix. Despite all the low-carb hype we hear these days, working muscles use carbohydrates for energy, and during exercise, the percentage of carbohydrates burned increases with intensity.
Our brains rely entirely on glucose (a simple carbohydrate) for energy. If you have ever experienced the sensation of being “hangry” (when you are so hungry that you get grumpy or have trouble concentrating), then you have felt your brain calling for glucose. As a survival mechanism, in the absence of adequate carbs/glucose, the human brain can also metabolize ketones to keep from starving.
Carbohydrates are stored in the liver and muscles as glycogen. When dietary carbohydrates are restricted, these stores are depleted. The basis of the ketogenic diet is to intentionally deplete these stores by severely limiting carbohydrate intake.
When there are no carbs available, the body is forced to rely more heavily on fat for energy. As fat is metabolized, ketones are produced. Ketones can be “recycled” for energy, but not very quickly. When they are produced faster than they are utilized, ketone levels in the blood rise and also are excreted in urine. This is ketosis.
There are several variations of the ketogenic diet, but traditionally it includes around 15 percent of calories from protein, and limits carbohydrate intake to 5-15 percent of total calories (about 20-75 grams per day), with the remaining 70-80 percent coming from fat.
What is the “keto flu,” and why does it happen?
The keto flu refers to a series of unpleasant side effects that many people experience as their carbohydrate stores are depleted and their bodies adapt to burning more fat. Symptoms include headache, nausea, bad breath, mental fogginess, muscle cramps, increased heart rate, fatigue, insomnia, feeling light-headed, and lethargy/fatigue.
It can take anywhere from a few days to several weeks for individuals to become “fat adapted” to the ketogenic diet, after which symptoms typically subside.
What are the benefits of this diet?
Obvious benefits of the keto diet include weight loss, often rapid, especially in the beginning. Fat makes foods taste good and is very satiating, so keto followers enjoy eating and not feeling as hungry as they may have on other diets.
There are a few short studies showing benefits such as improved glucose control, reduced insulin levels, and positive changes in cholesterol markers, even on a high-fat diet.
What are the risks of this diet?
Having the “keto flu” doesn’t sound like fun! The potential for dehydration and electrolyte imbalances can pose a challenge to the kidneys, and it is nutritionally inadequate (more on that below). We have decades of research supporting the fact that high-fat diets pose a risk to our cardiovascular health. Also, long-term compliance on such a restrictive diet is difficult to maintain, both practically and socially.
It sounds like this diet makes people miss out on a lot of nutrients. How can it be healthy?
It does. By eliminating or drastically reducing the consumption of many foods or food groups, long-term adherence to a ketogenic diet is likely to result in inadequate intake of many vitamins, minerals, and perhaps fiber.
As a registered dietitian, I cannot use the word “healthy” to describe this diet. It can be made healthier by including as many vegetables as possible and focusing on unsaturated fats (from nuts, oils, avocados, and fatty fish) while limiting saturated fats (from meats, butter, and other full-fat dairy foods). One good thing about this diet is that it cuts out simple sugars, which keeps people away from sodas, sweets, and fast food.
If an individual’s need for immediate weight loss is significant and this diet is appealing, then it may be an effective short term “fix.” But realizing that the ketogenic diet is not a healthy long-term solution, anyone planning to follow it would do well to have a follow-up plan for lifelong healthy eating. Consult your doctor before starting a new plan.