The ketogenic diet is another diet that is surrounded by a certain “magic weight loss” diet’s aura. Magic weight loss diets are to me the diets that are supposed to lead to a greater weight loss compared to other diets, even when calorie intake is the same.
The keto diet’s major selling point is the supposedly enhanced fat loss as a result of carbohydrate restriction to less than 50 g per day (just to give you an idea, in case you don’t count macros, 50 g per day equals to the carbohydrate content of 1 cup of cooked rice).
Carbohydrates are supposed to be “fattening” because they initiate the release of insulin, the hormone that is among other things also responsible for fat storage. However, there is one important error in reasoning when it comes to the fattening action of insulin.
It is important to note that protein consumption - well, essential amino acids to be more specific - also leads to insulin secretion that can cause even more insulin to be released compared to carbs. Based on the reasoning above, protein should also have a “fattening” effect and be eliminated on a keto diet. However, this is not the case. (If you want to learn more on the supposedly “fattening” effect of insulin, see my previous article: “The fattening hormone insulin - falsely accused”).
Another reason why ketogenic diet is supposed to be better for fat loss is because a higher level of fat oxidation is observed on ketogenic diet. Fat oxidation is a fancy term scientists use to tell that the calories that are burned by the body to provide the energy for living (organ function, movement, etc) come from fat. However, fat is not the only energy source for the body. The body can use carbohydrates - those you just ate or you have stored as glycogen in your muscle and your liver - to cover the energy needs or even protein from muscle can be used for energy generation (not good!).
An important point that is not considered or maybe not understood by those who claim that higher fat oxidation results in higher fat loss, is that fat loss is about the amount of energy burned and not if the energy comes from carbs or fat (well, ideally you shouldn’t burn muscle as fuel).
To make it a bit clearer here is a citation from a very interesting research study that compared the effect of a carbohydrate-restricted keto diet with the effect of a fat-restricted high carb diet on fat loss.
“Whereas carbohydrate restriction led to sustained increases in fat oxidation and loss of 53 ± 6 g/day of body fat, fat oxidation was unchanged by fat restriction, leading to 89 ± 6 g/day of fat loss, and was significantly greater than carbohydrate restriction (p = 0.002).”
Let’s reword the citation to make it easier to understand:
Keto diet led to a higher fat oxidation. Fat oxidation was unchanged on the high carb diet. However, the high carb diet led to a significantly higher fat loss than the keto diet.
How can it be?
The subjects following the high carb diet lost more fat because they burned more calories. However, as we know that the fat oxidation on the high carb diet didn’t increase, the most likely scenario is that the extra calories that were burned came from carbs.
At the end of the day, do you really care if the calories you burn come from fat or carbs if you lose more fat? To be honest, I don’t.
[Side note: If you are curious now why high carbohydrate diet may burn more calories, my speculation is that one of the possible reasons may be the different thermic effect of food for both nutrients. Carbohydrates require more energy to be processed by the human body than fat. Thus, a bigger percentage of the calories that are eaten as carbs are used for carbohydrate absorption, metabolism and storage compared to calories coming from fat.]
However, the study described above is not the only one that debunks the magic effect of the ketogenic diet. There was another brilliant study conducted on the effects of a ketogenic diet, in that subjects received exactly the same amount of calories and protein amount during both conditions, which isn’t typically the case with other research studies. Additionally, the subjects were trapped in the research facility, which meant they had absolutely no access to outside food. Visitors were allowed to meet with the study subjects in a common area, under supervision of nursing or research staff to avoid the exchange of food or beverages. Meals were consumed in a common area, under the observation of the research staff and participants were not allowed to leave the table during the meals. All meal trays were checked after consumption and any food that was not consumed was weighed and subsequent meals were adjusted for previously uneaten food. This was a really good controlled study!
After the subjects spent two months in the research facility, firstly following a high carbohydrate diet and then a ketogenic diet, body fat loss slowed down during the ketogenic diet period, which means that it is NOT better for weight loss.
Want to recap? Then watch this video on keto diet.
So, why do so many people think that the keto diet is better for weight loss?
Research studies: Previous research findings may have been confounded by not matching the calorie and protein intake. If one group eats fewer calories and more protein (protein has a higher thermogenic effect of feeding than other nutrients and is more satiating to some degree) then this group loses more weight. This is common sense.
Appetite suppressant effect: Another reason why the keto diet works for some people is the fact that the ketogenic diet seems to be more of an appetite suppressant (at least for certain individuals) than a higher carbohydrate diet. As such, it is possible that the ketogenic diet may be better, simply because some people lose their appetites and as a result eat less.
Stricter restrictions: Ketogenic diet puts very high restrictions on food choices. It automatically excludes most of the junk foods (as they usually contains carbs) and food many people are likely to overeat on (Yummy carbs!). Restrictions in food choices can not only lead to eating less, which is the major point of a diet, but also reduce the chance of overeating by eliminating the food that is tempting for most people. Keto diet seems to work well for people with an all-or-nothing mindset.
Take-home message:
There are no miracles, no magic diets… If you want to lose weight, the most important thing is to find a diet you can stick to.
Are you confused about different diets and how many calories you should eat?
Nutritional advice is great when it’s transparent, easy to understand and based on science. These are the principles I used for the design of my ‘Customized Macros Package’ that provides you
- Customized macros calculated individually for you
- Tables with food serving sizes and substitution options
- Meal suggestions and recipes
- ‘‘Fit Your Macros’ Calculator that will make it easy for you to fit the food you want into your macros
- Video tutorial that teaches you general principles of fitting macros and how to use the calculator