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Fact Check - The sense and nonsense of low-carb diets



In recent years, the low-carb trend has firmly made its way into the rhetoric surrounding "healthy" eating. Low-carb options on menus, advertisements for fitness and diet foods and popular diet gurus reinforce the idea that carbohydrates are best given a limited place in our diet. The low-carb trend manifests itself in various forms.


(Those who would like to get some more information about carbohydrates first - What are they? What are the different types? And what is their function? - can do so here).






In a low-carb diet, the intake of carbohydrates is greatly reduced.

The diet is recommended by some doctors for patients with Type 2 Diabetes. There are studies that show that, in some cases, it contributes to a positive effect on blood sugar, blood pressure and cholesterol. The important note to add here is that these recommendations always look at the quality of the carbohydrate sources, and mainly limit the simple carbohydrates. Thus, it is never about limiting carbohydrates in general. Moreover, this is always done under the strict supervision of a physician/dietician.


A second reason why people sometimes choose a low-carb diet is to lose weight. Its effect as a slimming diet is -as with all diets- based on a reduced calorie intake. So it will only work if you consume fewer calories in total than with your previous diet. The feeling of hunger is thought to be suppressed in three ways: (1) the higher proportion of protein provides a longer feeling of satiety (2) your body goes into 'ketosis' (it switches to burning fat), which is accompanied by an increase in the satiety hormones and (3) simple sugars promote the feeling of hunger, so by cutting these out the appetite is also reduced.


Many people start such a diet without professional supervision, making it difficult to maintain and causing you to quickly regain the pounds lost as soon as you switch back to your old eating pattern. Moreover -if you are not careful- it can lead to muscle breakdown, since carbohydrates are responsible for the hormones that stimulate muscle growth. So it is wrong to simply assume that an increased protein intake will prevent muscle breakdown. Furthermore, there may occur a shortage of a number of vitamins and minerals which are mainly found in carbohydrate-rich foods, such as folic acid, vitamin C, iron and magnesium. Due to the higher fat and protein intake, it can also have a negative impact on your kidneys and cardiovascular system.


A combination diet is based on the assumption that the different enzymes you need to digest carbohydrates, fats and proteins work against each other. Therefore, you need to keep certain food groups such as carbohydrates and proteins separate. This is based on very poor scientific research, since the different food groups are digested separately in your body, each using its own enzymes. It also claims that fruit after your meal causes fermentation and even putrefaction in your stomach. Fermentation is perfectly normal, however, and only if your intestinal flora is disturbed (by illness, stress or a one-sided diet) could this cause digestive problems. Apart from the fact that the diet is based on a misinterpretation of digestive physiology, it is also very impractical: foods often contain a combination of proteins, fats and carbohydrates, which severely limits the list of what you can eat. Therefore, it is very challenging to eat a versatile and varied diet, which can lead to significant nutritional deficiencies.



The paleo diet assumes that we should all eat like our ancestors, the primordial humans, did. It focuses on pure and unprocessed food -so far, so good-, but in a very rigid way: only meat, fish, eggs, vegetables, fruits, natural oils, nuts and seeds are allowed. The theoretical recommendations amount to 18 En% protein, 59 En% fat and only 20 En% carbohydrates. Just to recap, the general WHO guidelines are 15 En% protein, 30 En% fats and 55 En% carbohydrates. No distinction is made between saturated and unsaturated fats and meat consumption is unlimited, so you very quickly reach an excessive intake of saturated fatty acids (and let’s not forget the climate impact…). Cereals, potatoes and legumes are strictly forbidden. All dairy and calcium-enriched plant-based alternatives are out of the question, which means you can quickly build up a calcium deficiency. All these recommendations are made on the assumption that our metabolism is better adapted to the diet of the prehistoric man. However, there is no scientific evidence for this. On the contrary: recent research (Tito et al., 2015) shows that our gut flora has since evolved and is not even equipped for a prehistoric diet anymore.


The ketogenic diet (keto diet for short) focuses on a high intake of fats, a very low intake of carbohydrates and a slightly increased protein intake. As a result, your body does not have enough glucose available to use as fuel. The liver will use the fats and proteins (and reserves from muscle and fat tissues) to create ketones, which then serve as fuel for our body. It was used in the 1920s on epileptic patients, as the ketones created in the brain provide anti-epileptic qualities. They noticed weight loss in many patients, which is why it was eagerly picked up and marketed afterwards as the ultimate diet for losing weight. However, although it can have positive effects in epilepsy patients and you can lose weight initially, it is anything but healthy. Your body is forced into starvation mode and produces these ketones as a survival mechanism. Doesn't sound very wholesome, does it? There are also a number of unpleasant side effects such as nausea, headaches, dizziness, diarrhea, constipation, ... The diet is difficult to maintain, and can only be done correctly under strict guidance from a dietician or doctor, as the risk of nutritional deficiencies is very high.


In conclusion: certain diets, in certain circumstances and under proper supervision, can have a beneficial effect. However, most of the time they lead to an overly one-sided diet and the risk of deficiencies and damage to your metabolism. Moreover, they are often very impractical and therefore difficult to maintain, making you regain the weight just as quickly as you lost it.


We would like to end with a personal opinion. In our society, health is too often measured by our clothing size or our weight. There are very thin people who live unhealthy lives, just as there are people who are a bit heavier that are in excellent health. People that are overweight or struggling with obesity are at greater risk of various diseases, such as type 2 diabetes, cardiovascular disease and certain cancers. In addition, you suffer more easily from back and joint problems. We are not saying obesity isn’t a serious problem in our society, and that in those cases its necessary to take a close look at your eating pattern. But when you do so, it is best to put your health first. Weight loss is no guarantee of improved health, especially if you try to achieve it using one of the examples above. When you shift to a healthy, balanced eating pattern without restricting yourself, your body will naturally adjust to the weight that is ideal for you. That is why we would like to emphasize that our goal is to try to help you find a lifestyle that is healthy for your body ànd mind, and that it is not our intention to give you tips on how to lose weight. Because unfortunately, this social rhetoric is causing more and more people to develop an unhealthy relationship with food, which can lead to eating disorders and mental- and other health problems.


Do you have any questions or suggestions after reading this blog post? Feel free to leave a comment!



References

- Vlaams Instituut Gezond Leven, Koolhydraatarm dieet: https://www.gezondleven.be/themas/voeding/voedingsadvies-op-maat/levenswijze/populaire-di%C3%ABten/koolhydraatarm-dieet

- Vlaams Instituut Gezond Leven, Combinatiedieet: https://www.gezondleven.be/themas/voeding/di%C3%ABten-en-voedingspatronen/andere-di%C3%ABten/combinatiedieet

- Vlaams Instituut Gezond Leven, Paleodieet: https://www.gezondleven.be/themas/voeding/di%C3%ABten-en-voedingspatronen/andere-di%C3%ABten/paleodieet

- Vlaams Instituut Gezond Leven, Ketogeen dieet: https://www.gezondleven.be/themas/voeding/voedingsadvies-op-maat/levenswijze/populaire-di%C3%ABten/ketogeen-dieet

- Obregon-Tito, A., Tito, R., Metcalf, J. et al. Subsistence strategies in traditional societies distinguish gut microbiomes. Nat Commun 6, 6505 (2015). https://doi.org/10.1038/ncomms7505

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