The ketogenic diet is well established in medicine as interventions that effectively control epileptic seizures in children. However, its popularity for weight loss has skyrocketed in recent years. A Google Trends search from the years 2004 to 2019 clearly shows the greatest interest in the diet. However, the question remains: does the ketogenic diet allow people to lose weight or is it just another fad diet? Here are the clinical evidences for the ketogenic diet and weight loss.
How can we find out if the Keto Diet is better than a control?
In research, one of the best ways to assess the effectiveness of an intervention (such as diet) is with a randomized controlled clinical trial (RCT). This is because participants and researchers cannot control who gets what diet. This reduces selection bias and also aims to reduce the concentration of a particular characteristic in a group.
For example, if all participants with a hypothetical gene that allows them to adhere perfectly to weight loss diets are put in the keto diet group, then they will lose more weight than the control group, with few or no people with this gene. This will make it appear that the ketogenic diet was superior for weight loss since everyone in that group lost weight, but in reality, it was the highest concentration of people with this adherence gene. The complex randomisation methods used by clinical investigators help reduce the impact of this problem so that participants from both groups can be reasonably comparable and that all associated characteristics of recruited participants are randomized
A search of MEDLINE (the database administered by the National Library of Medicine, which indexes articles from scientific journals) shows that the number of randomized trials conducted on the ketogenic diet for weight loss has also increased over time.
What do RCTs say about the Ketogenic Diet for fat loss?
It is important to note that differences in weight loss do not distinguish differences in lean mass and fat loss. It’s worth noting, as carbohydrate restriction depletes glycogen stores (part of the lean mass), causing you to lose weight, but not necessarily fat.
Therefore, it is essential to also take into account differences in fat mass, which are often measured by other methods, such as DXA scans.
Another common limitation in research of weight loss is not energy or protein. For example, if participants in the ketogenic diet group consumed substantially fewer calories for some specific reason, and this is ignored, it will be difficult to conclude that the ketogenic diet exerted a unique metabolic effect that fueled fat loss when reduced. . Caloric intake was the real driver. Therefore, the combination of calories and other characteristics of an intervention, such as protein content, is vital in interpreting the utility of the findings. Brehm and colleagues found in two trials, one conducted in 2003 and the other in 2005, that When combined with calories, the keto diet still produces more fat loss than control groups, so there may be a metabolic advantage. on a ketogenic diet.
Another trial by Brinkworth and colleagues that also combined calories found that the ketogenic diet group experienced more fat loss than the control group. Although it is worth bearing in mind that these studies were also conducted in an obese population and did not adjust for protein content. However, the evidence on the superiority of the ketogenic diet for fat loss when combined with calories is mixed, as some studies have also failed to show a statistically significant difference in fat loss.
In four trials that combined protein intake and calorie intake between groups, there were no statistically significant differences in fat loss, so any single advantage attributable to diet may be mediated by protein content, however, It is also possible that the lack of differences may also be the result of the low sample size.
So why does the keto diet work for weight loss?
Insulin
There are several debated mechanisms as to why carbohydrate-restricting diets cause weight loss, and many proponents of carbohydrate-restricting diets argue that the main benefits of these diets are the metabolic benefits that result from reducing insulin, which They believe to be the main hormonal driver of fat storage. Many of these hypotheses are controversial, and studies that have investigated some of these mechanisms have shown mixed results, with the most recent support for the hypothesis coming from a Mendelian randomization study.
Hungry
Several trials report that participants feel less hungry and more satisfied with the keto diet. This may be due to the increased protein content in the diet, as protein is known to be one of the most satiating macronutrients. However, many ketogenic diets that are also low in protein still produce a satiating effect. So while proteins may contribute to a satiating effect, it does not appear to be responsible for all the satiating effects of diet. A systematic review hypothesized that increased satiety was the result of increased levels of ketone bodies in the blood, and one article assumed that ketone bodies can change the structure of various hormones involved in the regulation of hunger. The satiating effects of the ketogenic diet may be driving the main benefits of the diet, leading to lower calorie intake and, therefore, greater fat loss.