If you want to lose weight, you can spend an eternity studying nutritional advice. Science knows exactly which diets have a chance of success
The world of dietetics can be confusing. Marketers and fraudsters want to sell us innovative products that promise weight loss, while bloggers offer proprietary nutrition systems that claim to make us slim down faster than with Ozempic. It’s a territory filled with endless advice, prohibitions, and rules. And if you’re not careful, you can easily get lost.
A few numbers for context: the percentage of Americans who follow a diet or eating regimen is very high—54%. The most common are high-protein diets and mindful eating. Social media influences dietary choices more than ever before—54% of respondents admit that Facebook, Instagram, and TikTok determine their diet choices.
At the same time, the largest study among U.S. residents showed that obesity among adults aged 20 and over was 41.9% between 2017 and 2020.
“Body weight is not a choice,” says geneticist and nutrition researcher Giles Yeo. At the University of Cambridge, he has been studying the genetic factors underlying obesity for over 20 years. He has summarized the most important research findings in the popular science books “Gene Eating” and “Why Calories Don’t Count.”
He says, “Some people are more attracted to food than others. They eat more and, as a result, weigh more. There are social and cultural reasons for this. But now we know how genes control our appetite and eating behavior. This is the genetics of body weight.”
This gives us something to think about. Are diets futile if body weight is genetically determined? And how is it possible that over 40 years, the number of adults with severe overweight has tripled to 12% of the world’s population, even though genes have remained the same?
The World Health Organization (WHO) defines overweight as a body mass index (BMI) exceeding 25—BMI is calculated as body weight divided by height (in meters) squared. With a BMI over 30, experts speak of obesity or severe overweight. Excess weight increases the risk of numerous diseases, including type 2 diabetes, heart disease, and stroke. That’s why this issue is constantly discussed in health policy and medicine.
The body mass index causes a lot of concern because some people let it dictate their entire lives. A low score becomes synonymous with a happy life—and a trigger for eating disorders. However, BMI has many shortcomings. For example, muscular people, according to WHO’s definition, may be considered overweight even if they don’t have an increased risk of metabolic diseases. And for many years, there’s been debate about whether overweight individuals actually have a longer lifespan than those with normal weight. But BMI is much easier to determine than many other body indicators, so medicine sticks to it.
The environment can promote healthy eating
Now let’s turn to genes. At first glance, every person, of course, is free to decide what and how much to eat. And those who consistently consume more calories than they burn will gain weight. But our eating habits aren’t so “free,” because hunger is influenced by genes. Certain variations of the so-called FTO gene are associated with obesity (FTO stands for “fat mass and obesity”). This has been shown by genetic analyses of tens of thousands of people of European descent. A person 1.70 meters tall with a variant of the FTO gene weighs on average one kilogram more than someone without this variant. This may seem insignificant, but the genome contains hundreds of other variants that control appetite and, consequently, affect weight. Researchers discover several more such cases every year.
However, you not only inherit genes from your parents but also, to some extent, inherit the environment. Babies don’t choose their homes. The environment can contribute to obesity, for example, if the family enjoys snacks and ready-made meals. Alternatively, the environment can promote healthy eating, such as when a kindergarten serves plenty of fresh fruits and vegetables. Epidemiology studies this so-called gene-environment interaction through twin studies. The result: body mass, whether underweight, normal, or overweight, is determined by genes and the environment by 40-70%.
Giles Yeo says, “For middle-class people, this figure is closer to 40%.” They have carrots and hummus in the fridge and are interested in healthy eating. On the other hand, households lower on the socio-economic ladder approach 70%. For example, because they live in areas where access to healthy food is limited. Or because they can’t afford or don’t want to buy fresh products. “Poverty has a huge impact on the development of genetic predisposition,” says Yeo.
Some people love to eat a lot but don’t gain weight. It’s believed they naturally have a faster metabolism. Could this be true? Indeed, people with higher body weight have a faster metabolism compared to those with lower body weight. After all, almost every cell in the body needs energy, and the more weight, the more energy the body requires. On the other hand, science has yet to find genes that determine a higher energy metabolism in some people compared to others.
Perhaps it’s a matter of methodology. It’s much easier to determine the connection between genes and hunger than between genes and metabolism. After all, it’s easier to measure how much a person eats than how much energy they metabolize. And where there’s more data, there’s more knowledge. Therefore, genes for metabolism with varying activity levels may still be found. Nevertheless, Yeo is convinced that metabolism doesn’t play as significant a role in the heredity of body mass as the genetic control of hunger by the brain.
It’s important to realize that genes influence body weight not through metabolism but through the brain. The hypothalamus controls vital body functions using hormones, including hunger and thirst, satiety, and body temperature. Knowing this makes it easier to judge the effectiveness of diets and healthy lifestyle campaigns.
Which diets are effective according to official science?
If you eat only pineapples, you’ll lose weight, that’s for sure. However, mono-diets like cabbage, egg, or pineapple diets aren’t recommended even for office workers. They’re too monotonous. We’re not talking about them because science doesn’t advise using them.
Instead, we focus on diverse nutrition and look for the basic principles of a successful diet. Successful means that participants lose an average of 5 to 10% of their weight and maintain it for at least one or two years.
Intermittent fasting is one of the most popular diets in the world, especially the 16:8 variant, where food intake is limited to an eight-hour window per day. Anyone who feels comfortable can follow this diet, but studies have been disappointing. Participants practically didn’t lose weight. Some studies recorded improvements in health indicators, while others found no effect.
The effect is more noticeable if participants reduce food intake daily, approximately two days a week. According to a meta-analysis of 11 studies, after two to six months, they lost 5 to 13% of their weight. However, diets that simply reduced daily calorie intake had a similar effect.
The Mediterranean diet is more of a dietary change: lots of fresh fruits and vegetables, fish, white meat instead of red, nuts, whole grains, few dairy products, and plenty of olive oil. Without additional calorie reduction, it doesn’t have a significant impact on body weight.
However, a Spanish study showed significant improvement in health indicators: over five years, people who followed the Mediterranean diet with plenty of nuts and olive oil had a 30% lower risk of cardiovascular diseases compared to the control group that followed a low-calorie diet.
Low-carb diets reduce the amount of carbohydrates. This excludes bread, cereals, rice, potatoes, fruits, sweets, honey, and fruit juices. In a typical European diet, 50% of calories come from carbohydrates. The Paleo diet reduces this share to 30%, while the Atkins or keto diet sometimes lowers it to 10% or less. Accordingly, the proportion of proteins and fats increases. Can you lose weight this way? Yes. Is it healthy? Well, not necessarily.
We’re entering the controversial territory of diet wars. Sugar or fat, which is more harmful?
Why do some diets help with weight loss?
Low-carb diets are based on the so-called carbohydrate-insulin model and claim that in the absence of carbohydrates, the body’s metabolism shifts into higher gear. The promise: you can eat as many calories as before, just consume more meat, fish, cheese, and vegetables. The metabolism burns them better.
A study conducted by the National Institutes of Health in Maryland (USA) suggests the opposite. Kevin Hall recruited 17 overweight men and analyzed their metabolism over eight weeks. For half the time, they received food with 25% carbohydrates, and for the other half—with less than 2%. The result: the energy metabolism on a low-carb diet was not as high as its proponents predicted. Kevin Hall states, “If you flip a coin and put people on either a low-fat or low-carb diet, trial after trial will show that both diets yield similar results.” Yes, low-carb diets help with weight loss. No, it’s not about metabolism.
There are other explanations for why some diets help with weight loss. Firstly, because they reduce calorie intake. The body receives fewer calories than it expends, as with intermittent fasting or the “eat half” diet. Secondly, because they’re rich in protein. Proteins are not digested as quickly as fats or sugars. They are better absorbed and last longer. Low-carb diets are also characterized by high protein content. “One calorie of protein satiates you more than one calorie of fat,” says Giles Yeo, “and one calorie of fat satiates you more than one calorie of carbohydrates.” Thirdly, due to fiber. Dietary fibers are plant components that reach the large intestine undigested, where bacteria break them down. This also causes a feeling of fullness. Yeo says, “If a new diet hits the market and falls into one of these three categories, there’s a real chance it will work and not be complete nonsense.” This statement gives us strength for the final stage.
Many diets help lose weight if you stick to them. But often, they don’t help maintain the weight. Here’s where a fork in the road occurs. Two paths lead to the summit. The first path implies even greater personal responsibility. This is the promise of personalized nutrition. You submit a DNA or stool sample and receive personalized recommendations. This is what nutrigenomics, also known as nutritional genomics, deals with. The path is quite profitable for the diet industry.
For science, it’s almost a dead end. More and more scientists and researchers conclude that the personalized nutrition industry isn’t ready to offer anything more useful than standard advice. There’s simply no convincing evidence of this field’s effectiveness yet.
Firstly, a single stool sample has very low informativeness since the microbiome constantly changes. Secondly, it’s still unclear what a “healthy” gut flora looks like. Thirdly, diet is just one of hundreds of factors influencing the microbiome. Jacques Ravel, a professor of microbiology and immunology at the University of Maryland, published an article detailing several studies that question the accuracy of laboratory stool tests—some failed to reliably identify bacteria in the gut.
Moreover, some laboratories participating in a U.S. study provided different results for the same sample.
The second path questions politics and society. The main assumption is that people simply can’t cope with this alone. The temptation of snacks and ready-made meals, which the industry makes appealing with its magic tricks, is too great. In recent decades, the environment has changed, not the genome. Today, people live in an environment that helps them gain weight.
Instead of re-educating overweight people, health policy should change environmental conditions. For example, by restricting advertising of sweets targeted at children. Also, by ensuring that ready-made meals and soft drinks contain less sugar and fat.
“Politics and society can make the environment less conducive to obesity,” says Ralph Hertwig, director of the Max Planck Institute for Human Development. For example, by introducing taxes on sugar and fat. Mexico, Denmark, and other countries have already tried this: in Mexico, soft drink sales dropped. In Denmark, fat consumption decreased, but the tax on saturated fats was later repealed without any lobbying. The WHO calls for a tax on sugar in soft drinks “to save lives.”
The environment can also be changed in our personal lives. “Make the things you want to eat more often more accessible,” says Hertwig. Put chocolate in a distant drawer and hummus closer at hand. In professional circles, this is called self-nudging.
Yes, diets can help healthy people lose weight. However, obesity is a chronic disease that often cannot be overcome without medical consultation. No one is to blame for this. Anything that doesn’t lead to long-term dietary changes can also be harmful. Those who unsuccessfully try to lose weight may face mental health issues. Fat-shaming and unrealistic beauty standards contribute to this. Therefore, excess weight also concerns so-called people with normal body mass: they can shed their prejudices. And the goal is to create an environment that doesn’t harm but helps.
