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Eat fat and lose weight! That's the ketogenic method for rapid weight loss. But how does it work compared to other diets and are there any risks?
The ketogenic diet was first introduced in 1924 to help control seizures in epilepsy patients, and later gained popularity as a method for weight loss in the 1970s.
Keto, as it is also known, is still used by people who want to lose weight.
But Sarah Hamdan, a dietitian based in New York City, says she wouldn't recommend anyone use a ketogenic diet (KD) for weight loss.
"My main priority is long-term efficacy and safety," says Hamdan.
A keto diet is low in carbohydrates and high in fat. And the idea is simple. You switch the body's fuel from sugar to fat.
Our bodies normally utilize glucose (sugar) to produce energy. Whenever blood sugar depletes, for instance during and after sport, fasting, or starvation, the body shifts to fats as a source of energy.
As with prolonged starvation, the keto diet puts the body in a state called ketosis — that's when the body runs on fat. The name comes from "ketone bodies," which are fat-derived compounds that the body relies on for fuel in the absence of sugars.
When you limit sugar intake drastically, you force your body to use all the stored glycogen, a form of sugar stored in the liver. And when that sugar is used up, the body turns to burning fat for fuel and, after a period, enters the ketosis state. It can take 2-4 days to enter ketosis.
The Standard Keto Diet (SKD) is the most common.
It limits your carbohydrates to less than 50 grams per day. That accounts for 10% of your total calories. The rest of your daily calories are split between 20% protein and 70% fat. Yes, that's right — 70% fat.
Other forms of the keto diet are more restrictive. For instance, carbohydrates can be limited to only 2% of your daily intake, your proteins down to 8%, and the rest is made up with 90% fat.
It's generally considered healthy for an average adult to consume 225-323 grams (8-11 ounces) of carbohydrates per day. That's 45-60% of your daily calorie intake.
Notice the difference? To put it in perspective, a small banana has about 24 grams of carbs and 1 cup of cooked rice has 45 grams of carbs.
If you exceed your daily allowed carbs, you risk losing the ketosis state, and the body will go back to burning sugar for fuel, which will effectively interrupt the diet.
The keto diet has been reported to be effective for weight loss, monitoring blood sugar in diabetic patients, and decreasing blood pressure and triglycerides (a type of fat).
But it is unknown whether the weight loss is directly due to ketosis, or a result of people reducing their consumption of sugar and their overall calories, or the high levels of protein in the standard keto diet, which makes you feel sated (full).
When the body switches from sugar to fat as a source of energy, it can lead to flu-like symptoms known as "keto flu." Symptoms include headache, nausea, and fatigue.
Keto flu is harmless for most individuals, and people usually get over it within two weeks.
Other side effects include muscle cramps and bad breath.
Constipation is also a common side effect because the diet is poor in high fiber foods, such as whole grains, fruits and vegetables. Cutting out fruits and vegetables can lead to vitamin and mineral deficiencies.
New York dietician Sarah Hamdan says she is concerned about long-term health issues, such as "an increased risk of liver disease, kidney stones, osteoporosis and gout."
"Ketone bodies are produced by the liver," says Hamdan. "That can put pressure on the liver, which in turn can cause liver disease. And a high protein content can sometimes affect our kidneys."
Studies have suggested that keto diets may raise cholesterol, and levels of C-reactive proteins, which your body produces in response to an inflammation. C-reactive proteins are known as inflammatory biomarkers.
"The increase in inflammatory biomarkers is very concerning because we know that inflammation puts a lot of stress on the body and that it is associated with a lot of diseases like heart disease, diabetes, and obesity," says Hamdan.
But any side effects that occur will depend on the exact profile of the keto diet, says Roman Müller, a professor of nephrology at Cologne University Hospital.
"That goes for the type of fats contained in the diet and their effects on cholesterol and the liver, or potentially negative effects of a high protein intake on the kidney," says Müller, who is researching the effects of ketogenic diets as a treatment for kidney disease with his colleague, Dr. Franziska Grundmann.
Hamdan says links between the consumption of high saturated fats, such as high-fat meat, butter, and processed cured meat, and an increased risk of heart disease is "undeniable."
"The combination of high-fat food with a very low consumption of nutrient-dense foods, such as vegetables and fruits, can put a healthy heart at risk in the long term," she says.
Müller, however, says there are no reliable data on any potential cardiovascular risks.
"There are contradictions in the available data from trials, for instance regarding risk factors like 'bad' cholesterol," says Müller. "But it's thought that any risks would depend on the type of fat used in the diet, as well as any genetic predisposition to those conditions."
The keto diet has recently grown in popularity, but it doesn't really differ from other weight loss programs.
Several studies have suggested that people on keto diets lose weight rapidly at the beginning, but that later on there is very little difference between the weight they lose on keto compared to what they would lose on any other diet.
In fact, Müller says no diet has been shown to be superior to others when it comes to weight loss.
Grundmann adds that restrictive dieting can mess up your metabolism, even if you go back to your old eating habits. She says keto diets are similar to most other weight-loss diets and that "stopping a keto diet can lead to a significant regaining of weight."
When it comes to ketogenic dieting, the scientific community is still short on evidence, and some say more research is needed before it will be possible to draw any firm conclusions.
In any case, it is always best to consult your doctor and a nutritionist for personal advice if you are considering a diet for weight loss, perhaps especially if you're considering a restrictive diet such as keto.