Is "cutting on carbs" necessary during body fat reduction? Part III

There are many theories about the possibility of manipulating the intake of energy and particular macro nutrients during body fat reduction. However, there's no doubt that the conviction, according to which if you want to decrease the level of fat in the body, you have to limit the intake of carbohydrates – in the meaning of really big restrictions, has become very popular. Is such belief right? Well, taking under consideration available data – it may be doubtful.

You should definitely read:

Is “cutting on carbs” necessary during body fat reduction? Part I

Before you read this article

This article is a continuation of the topic initiated and described in two previous articles, in which there were aspects of manipulating the intake of non-protein calories during body fat reduction. In those articles I wrote about the methodology of scientific studies, in which the superiority of the diets limiting the supply of carbohydrates over diets with more balanced layout of macro nutrients was presented, paying attention to their serious flaws. I also described the aspects connected with hormonal conditioning, which accompany the carbohydrate and fat restrictions, in relation to the intriguing aspect of insulin resistance. In that case I presented the results of an interesting study, in which the limit of fat (and the increase of carbohydrates) in diet caused the improvement of insulin sensitivity. Remembering about the importance of the mentioned circumstances, I would recommend the readers of this article to start their reading with the linked articles:

Is "cutting on carbs" necessary during bodyfat reduction? Part I

Is "cutting on carbs" necessary during bodyfat reduction? Part II

The reality of modern studies

Scientific studies, in which various diets and their influence on the body composition are compared, usually have multiple limitations. One of their biggest flaws is poor control of realising the assumptions of particular diets by their users in practice. It is caused by the fact, that the volunteers aren't usually under the observation of the authors of the study for 24 hours a day. They usually get the recommendations and go home with instructions of what to eat and how to make notes of what they ate each day. Regular consultations with the specialists, which often take place during the experiment, as well as the regular measurements of the results, are a big help. But, you have to agree that such solutions cannot be compared to the options when all the volunteers are under constant control of the scientists throughout the trial. Unfortunately, there aren't many tests like that, because they are expensive and demanding, and it's much harder to find the volunteers who would like to take part in them...

Super-exact experiment

The circumstances mentioned a second ago may influence the credibility of the scientific studies. For example, in a situation when it's hard to control the realisation of the nutrition suggestions, the volunteers are more eager to follow the diets, which:

  • are closer to their culinary preferences,

  • let them control hunger better (although this aspect is an objective advantage for a particular diet – however, it's not always the subject of the study),

  • are less time- or technique-demanding.

Therefore, if there is any kind of experiment in the world of science, which is done in a maximally controlled way, we should treat its results as very precious. And, fortunately for the matter of the decribed issue, i.e. the influence of carbohydrate restrictions (compared to fat restrictions), there are some studies we can base on. Not so long ago the data from the experiment, which compared the influence of low-fat and low-carb diet on the tempo of the loss of body fat, were published.

19 obese people took part in that experiment. The volunteers were “locked” in a hospital and the research was done in the metabolic chamber, thanks to which the authors could monitor the exact processes in the participants' bodies. It was possible to control what the people ate, but also how they behaved, how much oxygen they absorbed and what they excreted! The authors of the study decided to set how the energetic substrate metabolism is changing in case of low-carb diet, and how it is changing in case of low-fat diet, they also wanted to know which diet promotes burning the reserve fat. Both diets provided the same amount of energy, the differences only concerned the layout of macro nutrients.

What did they find out?

The results of the experiment were following:

  • limiting the intake of carbohydrates also caused the use of lipids in the energetic processes. However, the problem is, that those were mostly lipids from food. At the same time, the use of carbohydrates was lower.

  • Low-carb diet caused significant decrease of body mass, but it mostly resulted from... losing water!

  • For change – what will be a surprise for many people – the volunteers lost more body fat when they were assigned to the low-fat diet. In case of this nutrition option, the loss of gathered lipid reserves was 89 +/- 6 g per day. For comparison, when using the low-carb diet, burning of reserve fat was only 53 +/- 6 g per day, i.e. it was significantly smaller.

You can read more about this study under the link below:


The results of the study mentioned above may seem surprising in the light of popular convictions concerning the nutrition interventions that we have to take in order to lose excessive body fat. The mentioned data turn out to be even shocking if we take under consideration that they concern obese people (it is believed that in case of obesity the low-carb diet is more efficient). Obviously, it is only an individual study and it does not undermine the efficiency of low-carb diets, but the conclusions drawn from it are a strong counter-argument against the belief, according to which we have to “cut down on carbs” to reduce body fat. The calorific balance is the key factor in the process of losing weight, although it may happen that in this context, one calorie is not equal to another calorie, and that such disproportion doesn't look as the LowCarb followers would like it to look.