To find out, identical twins and doctors Chris and Alexander van Tulleken undertook an unusual experiment. One gave up fats, the other sugar. The results were surprising and reveal more than you might think.

Brothers with identical genes, but different dietary approaches

Chris and Alexander shared more than just genes – they are both doctors, have similar lifestyles and dietary preferences. Despite this, Chris gained more weight than Alexander during his stay in the USA. This prompted them to explore how diet influences body weight.

As part of a BBC program, they decided on an experiment: Alexander eliminated almost all carbohydrates (sugars) from his diet, while Chris cut out almost all fats. Each ate as much as he wanted, with no restrictions on quantity, but one ban – for Alexander it was sugars, for Chris, fats.

First-hand experiences: sugar versus fat

Alexander, on a sugar-free diet, was able to eat meat, fish, eggs, and cheese. However, he reported a lack of energy, fatigue, and unpleasant breath. Within a month, he lost 6 kilograms but didn’t feel great.

Chris, who ate fat-free food, constantly felt hungry and often reached for snacks. Fat-free food didn’t satisfy him, but he still lost 2 kilograms.

The scientific view: what does research say?

Research shows that both low-carbohydrate and low-fat diets can lead to weight loss. A Stanford University study from 2018 showed that there is no significant difference in weight loss between the two diets. The more important factor is an individual's ability to stick to their chosen diet.

Another study showed that women with insulin resistance lost more weight on a low-carbohydrate diet than on a low-fat diet. This suggests that an individual's health condition may affect the effectiveness of a particular diet.

The combination of sugar and fat: a dangerous trap

The van Tulleken brothers found that it's not just sugar or fat alone that causes problems, but their combination. Foods containing both – like chocolate, ice cream, and fries – strongly affect the brain's reward centers, which can lead to overeating.

The modern food industry often combines sugar and fat, as this combination stimulates appetite and increases cravings. This can lead to increased body weight and health issues.

Balance and moderation are key

Instead of focusing on eliminating one group of nutrients, it's important to seek balance. A healthy diet includes moderate intake of all macronutrients – carbohydrates, fats, and proteins – with an emphasis on unprocessed foods.

It is also important to listen to your body and avoid processed foods that combine sugar and fat. Such foods can influence our eating habits and health.