October 15, 2026, 3:52 pm | Read time: 6 minutes
When people want to lose weight, they often think of a diet first. But with the wide range of options like intermittent fasting, low carb, keto, and many other dietary forms, it’s anything but easy to keep track. Additionally, many diets promise particularly quick or long-term success. An international team of experts has therefore evaluated scientific research on various weight loss strategies and derived 15 recommendations from it. The results show what really matters when losing weight–and which common beliefs cannot be scientifically confirmed.
Experts have scientifically compared various diets
An international team of experts led by nutrition scientist Alan A. Aragon examined which diets help with long-term weight loss and how to maintain as much muscle mass as possible. The scientific statement was published on October 13, 2026, in the journal “Journal of the International Society of Sports Nutrition.”1
For this, the experts evaluated previous studies, primarily with physically active adults and athletes, as well as additionally with overweight individuals. The publication contains 227 literature references. The number of individual studies considered is not specified.
These are the results of the scientific evaluation
Intermittent fasting leads to similar weight loss as a conventional diet where fewer calories are consumed daily.
A previous evaluation of several studies found that people with intermittent fasting lost an average of 0.94 kilograms more body weight and 1.08 kilograms more body fat after six months than comparison groups with daily calorie reduction. However, the differences were too small to be of practical significance for health. In studies lasting more than six months, no statistically significant differences were detectable. However, the exact form of fasting is important: With alternate-day fasting, the risk of muscle mass loss is higher than with time-restricted eating (TRE). The latter mainly helps to eat slightly less spontaneously without continuous calorie counting.
Low Carb or Low Fat?
Even a significant reduction in carbohydrates does not provide a decisive advantage over a low-fat diet in the long term. A review of 61 controlled studies showed that people on a low-carb diet lost an average of one kilogram more weight in studies lasting three to less than twelve months. In studies lasting at least twelve months, the difference was less than one kilogram. If calorie and protein intake are kept exactly the same, both low carb and low fat lead to the same fat loss. The rapid weight loss at the beginning of a low-carb diet is mainly due to the loss of stored water and carbohydrates (glycogen).
Ketogenic diets, where no more than 50 grams of carbohydrates are consumed daily, can also help with weight loss. However, studies more often show a stronger decline in fat-free body mass, which includes muscles, water, and other body components. Especially in short studies, changes in water balance can influence the results.
Crash Diets: Quick Weight Loss, but No Long-Term Advantage
Particularly strict diets with less than 800 calories daily can lead to a weight loss of about 1.5 to 2.5 kilograms per week.
A previous evaluation of several studies showed that people on such diets initially lost an average of 16.1 percent of their initial weight. With less strict low-calorie diets, it was 9.7 percent. In long-term follow-up, the weight loss was still 6.3 and five percent, respectively. The difference was not statistically significant. Very strict diets can also promote muscle mass loss and lead to insufficient intake of important nutrients. Such extreme diets are usually based on medical formula products. To minimize the yo-yo effect afterward, experts recommend a structured transition phase of three to eight weeks, during which solid food is gradually reintroduced.
Protein and Strength Training Help Preserve Muscle
The experts emphasize that sufficient protein and strength training can limit muscle loss during a diet. For the general population, they recommend 1.2 to 1.6 grams of protein per kilogram of body weight daily. For a person weighing 70 kilograms, this corresponds to 84 to 112 grams of protein per day.
Those who regularly engage in strength training and want to build muscle can benefit from 1.6 to 2.2 grams per kilogram. For 70 kilograms, that would be 112 to 154 grams daily.
For already lean, well-trained strength athletes who want to maintain as much muscle mass and other fat-free tissue as possible during a diet, the authors even suggest 1.9 to 3.2 grams per kilogram of body weight. However, these particularly high amounts are not a general recommendation.
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Eating More Often Doesn’t Automatically Help with Weight Loss
Whether someone eats two, three, or more meals a day has no decisive impact on weight loss, according to the evaluated research. For physically active people, however, it may be beneficial to distribute protein across at least three protein-rich meals. The total protein amount per day remains more important.
Water, digestion, and simultaneous muscle building can obscure fat loss on the scale. Therefore, experts recommend observing weight development over seven to 14 days and additionally measuring, for example, waist circumference. If weight remains unchanged for a longer period, decreased energy expenditure may also play a role. The fear of a permanently ruined metabolism (“starvation mode”) is scientifically unfounded: The metabolic slowdown is minimal and almost completely disappears once weight stabilizes. Phases with stable weight can also help practice maintaining the weight already achieved.
How Reliable Are the Experts’ Recommendations?
The analysis provides a broad overview of research on different weight loss strategies. However, there are some limitations.
The results cannot be universally applied to all people. Especially with protein intake, it is crucial for which groups the respective amounts were studied. Additionally, the studies differed in terms of duration, calorie intake, and accompanying training programs. Short studies do not allow for reliable conclusions about whether weight loss can be maintained over years.
The authors also did not use a uniform evaluation method to determine how reliable the scientific evidence is for each individual recommendation.
Several authors report professional connections to the nutrition and dietary supplement industry. These include paid consulting activities, lectures, and financial support for research projects. The International Society of Sports Nutrition (ISSN) is also supported by companies that manufacture or sell dietary supplements. However, the authors stated that they received no external funding for the current publication.