by Although nutrition has made significant progress in recent years—such as recognizing the harm caused by trans fats—it is surprising that, even in the academic field, there is an ongoing debate about the most effective diet. Spoiler alert: any of them can work as long as the diet matches your preferences and allows for better consistency.
In other words:
“Do we need diet books and programs that instruct us to eat fruits and vegetables, moderate refined sugar and alcohol, or nutritional coaches who scare their audiences on social media with lists of allowed and prohibited foods?”
– What Nonsense, Pseudoscience and Other Absurdities [1]
Of course, the answer to both questions is overwhelming. However, this does not prevent a growing number of self-proclaimed health experts from pointing the way – often with a link to buy their advice or products – towards healthy eating.
In recent years, especially on social media, we have seen claims such as the low carb diet is ideal for weight loss, intermittent fasting is the best for longevity, the carnivore diet can cause disorders psychiatric cure, and the vegan diet can save. planet, and even relieve migraines.
While I’d love to explore the data behind each of these claims, the main focus of this article is a not-so-new industry trend: diets based on your genetics derived from DNA testing. In a word, nutrigenetics
How will these tests work?
Typically, the consumer orders the test online, collects a saliva sample and sends it to the company. The company extracts DNA from the sample and analyzes it for genetic variants associated with increased risk of disease, regulation of specific traits, or health conditions. Among the most common services offered by these companies are genetic kits related to physical fitness (such as sports performance and injury risk), pharmacogenetics (personalized drug treatment), and nutrigenetics (weight control, food intolerances, and sensitivities).
According to s review published in 2020, nutritional tests aim to act as a compass, guiding users to make more informed and healthier decisions.
“Standard dietary guidelines are based on the average population and are used to prevent deficiencies, not to optimize levels of personal fitness, health and well-being. You are unique, so should your nutrition (diet).”
– Nutri Genetix
However, this assertion blurs the line between science and marketing.
For example, Nutri Genetix, a company that markets these tests and develops personalized food shakes based on the genetic results – which I would call a double win – claims that its tests are nutritionally based. This emerging field examines how genetics influence the processing and metabolism of various nutrients.
They promise that the results of their tests can:
- Reveal, based on your genetic changes, your ability to use, process and absorb different nutrients (like caffeine and sodium).
- State your specific needs for various micronutrients (vitamins and minerals).
- Assess how much endogenous antioxidants you can produce.
- Identify which macronutrient (fat, protein, or carbohydrate) is most likely to cause weight gain.
- Detect food allergies.
There is some truth to these claims, at least for caffeine, whose metabolism is primarily affected by an enzyme called cytochrome P-450. Genetic variations in this enzyme can alter its activity, speeding up or slowing down metabolism. A a systematic review published i Nutrients investigated how single nucleotide polymorphisms (SNPs) are [2] the impact of habitual caffeine use and the ergogenic and anxiogenic effects of caffeine. The review found strong evidence that SNPs in all three genes are associated with habitual caffeine consumption.
Although there is substantial evidence of how genetic variability affects caffeine metabolism, this does not necessarily mean that genetic polymorphisms related to its metabolism will similarly affect other substances. By assuming that genetics is the basis for personalized nutrition, these nutritional tests often fail to distinguish between established research and preliminary studies that require replication and quality evaluation. Hasty generalizations are often made by selling a nutritional test, drawing conclusions from a small or unrepresentative sample and false analogies when two cases have superficial similarities but significant material differences.
What is the evidence for weight loss?
To address this question, a randomized clinical trial published in Nature Communication test the following hypothesis: Will participants assigned to a diet tailored to their genotype (responses to fat or carbohydrates) lose more weight over 12 weeks than those assigned to a diet not aligned to their genotype?
Participants were between 18 and 75 years of age, non-smokers, overweight (BMI between 27 and 45 kg/m²), and had no conditions or medications affecting body weight or metabolism. They were stratified by genetic predisposition based on the characterization of 10 SNPs, which favored diets rich in carbohydrates or fats.
Of 145 participants recruited and randomized, 16 were lost to follow-up, and 7 were excluded due to genotyping errors or missing weight data. Therefore, the final analysis included 122 participants, who were randomly assigned to a high-fat or high-carbohydrate diet and divided into four analysis groups:
- fat respondents receiving a high-fat diet
- Fat responders receiving a high-carbohydrate diet
- Carbohydrate responses receiving a high-fat diet
- Carbohydrate responses receiving a high-carbohydrate diet
The mean age was 54.4, with a BMI of 34.9, classified as Grade 1 obesity, predominantly female and Caucasian, with a higher prevalence of fat-responsive genotype. Both diets were designed to create a caloric deficit of 750 kcal, reducing weight by slightly more than a pound weekly. The only difference between the diets was their nutrient composition; the high-carbohydrate diet got 20% more calories from carbohydrates, and the high-fat diet got 20% more from fat.
During the 12-week intervention, volunteers participated in weekly group sessions covering a variety of food-related topics, from meal planning to behavior changes. Participants were instructed to weigh themselves daily and send photographs of their weight to the mediators before each session. Although the sessions were originally planned to be held in person, most were held remotely due to the COVID-19 pandemic.
Results
- Weight loss did not differ between genotype-aligned diets and those that did not. The change in weight of fat responders was similar on both high-fat and high-carbohydrate diets. The same pattern was observed among the carbohydrate responders.
- There were no significant differences in body fat and anthropometric measurements, such as hip and waist circumference, between genotype-matched and genotype-mismatched diets.
- Changes in hunger, satisfaction with the intervention, and food cravings and preferences did not differ between congruent and incongruent diets.
Based on these results, the authors wrote
“We found no difference in WL [weight loss] between individuals on the genotype-concordant vs. genotype-inconcordant diet.”
Among the most obvious limitations of the study are three main questions:
- There were challenges with participant adherence. 39% in the high carbohydrate diet and 66% in the high fat diet followed the recipe and diet preparation they were asked to follow.
- The sample size was small, which limited the detection of small but significant clinical differences, ie body fat.
- The authors acknowledge that the genetic algorithm used to classify individuals as fat or carbohydrate responders was based on retrospective and moderate-sized studies that may have resulted in false positive stratification.
Finally, there are two points to consider, although they do not change the results obtained. First, the “high-fat” diet contained more carbohydrates than fat, suggesting that participants with a fat-responsive genotype did not receive a sufficiently tailored intervention. Secondly, there could be a conflict of interest. Both authors are shareholders and employees of Weight Watchers, who do not offer or believe in the value of the genetic test for weight loss.
Does this mean the results are not reliable? It is not necessary. However, these factors emphasize the need for caution in interpreting the results and emphasize the importance of awaiting future trials to confirm or refute the validity of these findings.
The bottom line is that although nutritional companies present themselves as scientific, their aggressive marketing is full of anecdotal consumer experiences. We currently lack strong evidence to support the effectiveness of nutritional testing for weight loss. Until new evidence emerges, I suggest you avoid spending your hard earned money on these weight loss promoting products, not by offering customized ‘foods’ to help or prevent weight loss but by impose a restricted calorie diet.
[1] The authors, microbiologist Natália Pasternak and journalist Carlos Orsi describe this insight.
[2] SNPs are genetic variations in a single base pair in the DNA sequence.
Sources: The Personalized Nutrition Study (POINTS): evaluation of a genetic-informed weight loss approach, a Randomized Clinical Trial. Nature Communications DOI: 10.1038/s41467-023-41969-1.
Genetics of caffeine consumption and responses to caffeine. Psychopharmacology. DOI: 10.1007/s00213-010-1900-1.
