Is it necessary to cut out carbohydrates to lose weight?
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When it comes to losing weight, one of the most widely used strategies is to cut down on carbohydrates, the basis of what are known as ‘low-carb diets”. But does it really make sense to restrict this nutrient? And in what proportion?
Throughout this article we'll explore the issues behind this association between cutting carbohydrates and weight loss, as well as its real impact on the process.
Carbohydrate Consumption, Insulin and Weight Loss
After a meal rich in carbohydrates (but also protein), our levels of insulin, a hormone produced in the pancreas, will rise.
Among other functions, insulin promotes a temporary reduction in the oxidation (‘burning’) and mobilisation of fat. In this sense, the idea arose that by reducing carbohydrate consumption and the consequent production of insulin, we will promote a more constant ‘fat burning’ over time, which will naturally favour weight loss.
On the other hand, a high consumption of carbohydrates will promote weight gain due to an increase in insulin levels and a greater accumulation of fat in adipose tissue.
It should also be emphasised that there is no clear consensus on what defines a low-carbohydrate diet. Several studies define a low-carbohydrate diet as a percentage of total energy value (TEV) or total daily carbohydrate intake, as follows:
- Very low carbohydrate (<10% VET) or 20 to 50 g/day
- Low in carbohydrates (<26% VET) or less than 130 g/day
- Moderate in carbohydrates (26%-44% VET)
- High in carbohydrates (>45% VET) (1)
Why can cutting back on carbohydrates work for weight loss?
Drastically reducing your carbohydrate intake can lead to rapid weight loss, due to essentially 3 factors:
1. You'll go into an energy deficit
If you significantly reduce your intake of carbohydrates, the macronutrient that contributes most to your daily energy intake, it's understandable that you'll lose weight.
However, this loss is not due to the removal of carbohydrates, but rather to the calorific deficit created, and creating a daily energy deficit is the essential principle of weight loss.
In addition, there are many foods with high palatability (tastier foods) and calorie density that have a high amount of carbohydrates (and fat). By limiting their consumption, there is likely to be a decrease in total calorific intake.
2. You'll lose a lot of intramuscular water
Every gram of glucose (the basic carbohydrate molecule) is combined with 3-4 grams of water to form energy reserves (called muscle and liver glycogen).
This means that by cutting down on carbohydrates, our glycogen reserves will drop dramatically, leading to a rapid loss of body water.
For this reason, the first phase of weight loss is not always a good one, as it is characterised by a rapid loss of body water rather than a significant loss of fat mass. (2)
3. You'll probably increase your fibre and protein intake
When a person cuts down on carbohydrates, it's common to see a concomitant increase in the consumption of protein and fibre.
Considering that protein is the macronutrient that induces greater satiety, it's understandable that it can also lead to a reduction in total spontaneous calorific intake at the end of the day and a greater energy deficit.
What does science tell us about cutting down on carbohydrates?
A natural consequence of starting a diet lower in carbohydrates is greater fat oxidation. However, it's important to realise that an increase in fat oxidation in response to a cut in carbohydrates is not synonymous with a greater loss of total body fat.
In fact, a selective reduction in dietary carbohydrates (low-carb diet) resulted in decreased insulin secretion, increased fat oxidation and increased body fat loss compared to a baseline isocaloric diet.
In contrast, selective isocaloric fat reduction (low-fat diet) did not cause significant changes in insulin secretion or fat oxidation compared to the baseline diet, but demonstrated a more marked loss of body fat than during the carbohydrate-restricted diet. (2)
Ultimately, although the macronutrient ratio is important, energy balance will always be the most important factor when it comes to weight control.
Conclusion and Take-Home Messages
Reducing carbohydrate consumption is a natural consequence of losing weight. However, it is essential to realise that this reduction is much more due to the need to create a calorie deficit, the basic principle of weight loss, and not to gain a metabolic advantage by reducing insulin levels.
This is because reducing protein intake is probably not the best option, as it is the most satiating macronutrient and helps maintain muscle mass during a calorie restriction phase and considering that the recommendations for fat consumption are around 20-35% of total daily calories, we will also be limited when it comes to reducing this macronutrient.
Furthermore, it's important to realise that the calorie deficit must be maintained over time to promote lasting results. This means that whatever nutritional strategy is used, it must ensure that the person is able to consistently adhere to the diet plan to achieve successful weight loss and, subsequently, weight maintenance in the long term.
Therefore, people who feel better and find it easier to adhere to a low-carbohydrate diet in a weight-loss context can do so, if they do so in a conscious and planned way, so that nutritional deficiencies don't arise.
Bibliography:
1- Oh R, Gilani B, Uppaluri KR. Low-Carbohydrate Diet. 2023 Aug 17. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan–. PMID: 30725769.
2- Hall KD, Bemis T, Brychta R, Chen KY, Courville A, Crayner EJ, Goodwin S, Guo J, Howard L, Knuth ND, Miller BV 3rd, Prado CM, Siervo M, Skarulis MC, Walter M, Walter PJ, Yannai L. Calorie for Calorie, Dietary Fat Restriction Results in More Body Fat Loss than Carbohydrate Restriction in People with Obesity. Cell Metab. 2015 Sep 1;22(3):427-36. doi: 10.1016/j.cmet.2015.07.021. Epub 2015 Aug 13. PMID: 26278052; PMCID: PMC4603544.
Author:
Rita Lima (CP.3003N)