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The truth about keto diets and rapid weight loss

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Obesity is on the rise in today’s society, no wonder why so many people want to lose weight. But what’s the price they are willing to pay? Most people think a good diet is one that would bring down their weight numbers quickly, but is that so? Weight loss is more than just numbers on a scale, and if you want results and a healthier body, there’s something else you need to pay attention to: your metabolism.

A tricky word, metabolism

So, what is metabolism? This simple word covers many events and internal processes your body does every day. Your metabolism is the way chemical compounds behave inside your body, and one special type of metabolism is that of energy. Energy metabolism dictates how you handle sugar, when do you start burning fat, and determines how strong, active and resistant you are. This is why some people talk about slow metabolism when it’s harder to lose weight, and fast metabolism in the opposite case.

According to a review by Nature, when people try to lose weight using restrictive diets such as keto diet, their metabolism starts burning energy from fat. After a while, their metabolism turns the attention to carbohydrates instead. So, since it’s suddenly showing preference to burn carbohydrates, the spare fat is stored in their belly. After that, and since keto diet is very difficult to sustain, people tend to stop dieting and weight regain starts, faster than ever because their metabolism has already made the switch. The only thing to avoid such rebound effect would be through physical activity and macronutrient regulations.

What’s more, there’s many people who combine keto diets with high-intensity cardio workouts. Keto diets consist of very low levels of carbohydrates and high consumption of healthy fats. They are considered to be efficacious for weight loss and have been proven to reduce hunger in their users. However, not consuming enough carbohydrates and giving your body a lot of cardio workout only results in one thing, and that is muscle loss. Since your body doesn’t have a rapid source of energy, it turns to your muscles, breaks them down, and obtain energy from their proteins. On the long run, this would further slow down your metabolism because, the less muscle you have, the less energy you will be able to burn.

Keto diets and insulin resistance

Another big problem about ketogenic diets is that there is controversy about the development of insulin resistance as a result of this restrictive regime. There are many studies, both in mice and humans, showing that this type of diet can result in insulin sensitivity problems. Insulin is an important hormone for your metabolism, it dictates how your body will use sugar because it basically helps your cells internalize and process sugar into energy. So, insulin is the one to blame for the appearance of high blood sugar and type 2 diabetes.

Keto diets, and any other low-carbohydrate, high-fat diet can potentially alter the way your organism responds to insulin. The cells in the liver and muscles become less sensitive to insulin, in a process called insulin resistance, which some people also call pre-diabetic state. But how does that happen?

It’s a solid fact, and scientists realized more than 40 years ago that fat can cause insulin resistance. When fatty acids are accumulated in the tissue of the liver and the muscle, the insulin receptor in the cells gets blocked by an enzyme called protein kinase C. Since insulin receptor is blocked, the cells no longer respond to insulin and the sugar starts accumulating in the blood. No wonder why hepatic steatosis is linked to type 2 diabetes.

Now that we know fat accumulation can result in insulin resistance, what can we say about keto diets? They are high-fat diets that gradually tells your body it should burn carbohydrates first, thus causing spare fat accumulation on the long run. It won’t be hard to conclude that this type of restrictive regime would likely end up in insulin resistance. And what’s more, it’s not only theory, there are many studies on the subject.

A study performed in the University of Amsterdam reported that people who used low-carb, high-fat diets –as in the case of keto diets- had higher blood sugar even when insulin was already increased. In contrast, people following conventional diets had a normal response to insulin, and thus their blood glucose was not so elevated. The authors explained that high-fat diets caused an increase in fatty acid concentration that suppressed the normal signal insulin gives the body to stop producing endogenous glucose.

Summarizing, keto diets and similar high-fat diets can cause an accumulation of lipids in the blood and tissues. Fatty acids trigger enzymes and block the insulin receptor. As a result, glucose starts to accumulate in the blood, and what’s more the body does not receive the signal to stop producing endogenous glucose. The final outcome worrying: hepatic steatosis and type 2 diabetes. And even if that didn’t happen to your neighbor, are you sure you want to roll the dice and take the risk?

So, let’s revise our understanding on the subject. A good diet is one providing fast results? Not necessarily. The best type of diet is one you can easily incorporate in your life for good, one you will feel comfortable with. You may lose weight with keto diets, you may feel less hungry, but what’s happening with your metabolism? Keto diets were designed for chronic kidney disease, epilepsy and other neurological problems, not for weight loss. So, before starting any restrictive regime talk to your doctor, dietitian or clinical nutritionist.

written by Riccardo Alessandro Migliorini


Greenway, F. L. (2015). Physiological adaptations to weight loss and factors favouring weight regain. International journal of obesity39(8), 1188.

Jornayvaz, F. R., Jurczak, M. J., Lee, H. Y., Birkenfeld, A. L., Frederick, D. W., Zhang, D., … & Shulman, G. I. (2010). A high-fat, ketogenic diet causes hepatic insulin resistance in mice, despite increasing energy expenditure and preventing weight gain. American Journal of Physiology-Endocrinology and Metabolism299(5), E808-E815.

Johannsen, D. L., Knuth, N. D., Huizenga, R., Rood, J. C., Ravussin, E., & Hall, K. D. (2012). Metabolic slowing with massive weight loss despite preservation of fat-free mass. The Journal of Clinical Endocrinology & Metabolism97(7), 2489-2496.

Samuel, V. T., Petersen, K. F., & Shulman, G. I. (2010). Lipid-induced insulin resistance: unravelling the mechanism. The Lancet375(9733), 2267-2277.

Bisschop, P. H., de Metz, J., Ackermans, M. T., Endert, E., Pijl, H., Kuipers, F., … & Romijn, J. A. (2001). Dietary fat content alters insulin-mediated glucose metabolism in healthy men–. The American journal of clinical nutrition73(3), 554-559.


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