While nutrition has made significant progress in recent years (such as the increased awareness of the harm caused by trans fats), it’s surprising that there’s still an ongoing debate, even in academia, about the most effective diet. Spoiler alert: Any of these can work, as long as it aligns with your preferences and allows for greater consistency.
In other words:
“Do we need diet books and programs that teach us to eat fruits and vegetables, cut back on refined sugar and alcohol, or do we need nutrition coaches on social media who scare their audiences with lists of allowed and forbidden foods?”
– What nonsense, pseudo-science and other nonsense [1]
The answer to both questions is, frankly, a resounding no. But that’s not stopping a growing number of self-proclaimed health experts from showing the right way to healthy eating—often with advice or a link to buy their products.
In recent years, especially on social media, we have seen claims that a low-carb diet is ideal for weight loss, intermittent fasting is best for longevity, a carnivore diet can cure psychiatric disorders, a vegan diet can save the planet, and even relieve migraines.
I’d love to dig into the details behind each of these claims, but the main focus of this article is on a not-so-new industry trend: diets based on your genetics derived from DNA tests. In a word, nutrigenetics
So how will these tests work?
Typically, a 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 that are linked to increased risk of disease, modification of certain traits, or health conditions. The most common services offered by these companies include genetic kits related to physical fitness (such as sports performance and injury risk), pharmacogenetics (personalized medicine), and nutrigenetics (weight management, food intolerances and sensitivities).
According to someone review The nutrigenetic tests published in 2020 aim to serve as a compass that guides users to make more informed and healthy decisions.
“Standard dietary guidelines are based on the average population and are used to prevent deficiencies, not to optimize personal fitness levels, health and well-being. You are unique and so should your nutrition (diet) be.”
– Nutrition Genetix
But this claim blurs the line between science and marketing.
For example, Nutrition GenetixA company that markets these tests and develops personalized food shakes based on genetic results, which I’ll call a win-win, claims that their tests are based on nutrigenetics. This emerging field investigates how genetics affects the processing and metabolism of various nutrients.
They promise that test results can:
- Uncover your ability to use, process, and absorb different nutrients (like caffeine and sodium) based on your genetic variation.
- Indicate your specific needs for various micronutrients (vitamins and minerals).
- Assess the amount of endogenous antioxidants you can produce.
- Determine which macronutrient (fat, protein or carbohydrates) is more likely to cause weight gain.
- Identify food allergies.
There’s 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, either speeding up or slowing down metabolism. systematic review published Nutrients How to investigate single nucleotide polymorphisms (SNPs) [2] influences habitual caffeine use and the ergogenic and anxiogenic effects of caffeine. The review found strong evidence that SNPs in three genes were associated with habitual caffeine consumption.
Although there is significant evidence that genetic variation affects caffeine metabolism, this does not mean that it will be similarly affected by genetic polymorphisms related to the metabolism of other substances. By assuming that genetics is the basis for personalized nutrition, these nutrigenetic tests often fail to distinguish between well-established research and preliminary studies that require replication and quality assessment. Selling nutrigenetic tests often makes hasty generalizations, extrapolates from small or unrepresentative samples, and makes false analogies where two conditions share superficial similarities but have important and relevant differences.
What is the evidence for weight loss?
A randomized clinical trial to address this question published inside Nature Communications We tested the following hypothesis: Would participants assigned to a diet tailored to their genotype (those responding to fat or carbohydrates) lose more weight over 12 weeks than participants assigned to a diet not tailored to their genotype?
Participants were between 18 and 75 years of age, nonsmokers, overweight (BMI between 27 and 45 kg/m²) and not taking any conditions or medications affecting body weight or metabolism. They were stratified according to a genetic predisposition based on the characterization of 10 SNPs and preferred diets rich in carbohydrates or fats.
Of the 145 participants recruited and randomised, 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 randomly assigned to either a high-fat or high-carbohydrate diet and divided into four analysis groups:
- Obese responders on a high-fat diet
- Obese responders on a high-carbohydrate diet
- Carbohydrate responders on a high-fat diet
- Carbohydrate responders on a high-carbohydrate diet
Mean age 54.4 years, BMI 34.9, classified as grade 1 obesity, predominantly female and white, higher prevalence of a fat-responsive genotype. Both diets were designed to create a calorie deficit of 750 kcal, resulting in weight loss of slightly more than 1 pound per week. The only difference between the diets was in their nutritional composition; the high-carbohydrate diet provided 20% more calories from carbohydrates, and the high-fat diet provided 20% more calories from fat.
During the 12-week intervention, volunteers attended weekly group sessions covering a variety of food-related topics, from meal planning to behavioral changes. Participants were instructed to weigh themselves daily and send photos of their weight to interventionists before each session. Although the sessions were initially planned to be held in person, most were conducted remotely due to the COVID-19 pandemic.
Results
- Weight loss did not differ between genotype-matched and nonmatched diets. Weight change in fat responders was similar on both high-fat and high-carbohydrate diets. The same pattern was observed in carbohydrate responders.
- No significant differences were found between genotype-matched and genotype-mismatched diets in terms of anthropometric measurements such as body fat and hip and waist circumference.
- Changes in hunger, satisfaction with the intervention, food cravings, and preferences did not differ between concordant and inconcordant diets.
Based on these findings, the authors wrote:
“We found no difference in WL [weight loss] “The difference between individuals on genotype-compatible and genotype-incompatible diets.”
The most obvious limitations of the study include three main issues:
- Participants had difficulties in compliance. 39% of those on a high-carbohydrate diet and 66% of those on a high-fat diet followed the recipe and diet preparation requested of them.
- Small sample size limited detection of small but significant clinical differences, e.g. 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, which may have led to false-positive stratification.
Finally, there are two points to consider, although they do not change the results found. First, the “high fat” diet contained more carbohydrates than fat, suggesting that participants with a fat-sensitive genotype did not receive an adequately tailored intervention. Second, there is a potential conflict of interest. Two authors are current shareholders and employees of Weight Watchers and do not currently believe in or offer this value. genetic testing for weight loss.
Does this mean that the findings are unreliable? Absolutely not. However, these factors highlight the need for caution when interpreting the results and underscore the importance of awaiting future trials to confirm or refute the validity of these findings.
In conclusion, while nutrigenetics companies present themselves as scientific, their aggressive marketing is filled with anecdotal consumer experiences. We currently lack solid evidence supporting the effectiveness of nutrigenetic testing for weight loss. Until new evidence emerges, I would suggest that you avoid spending your hard-earned money on these products, which at best promote weight loss, not by offering ‘foods’ specifically designed to help you lose weight or prevent weight gain, but rather by simply following a calorie-restricted diet.
[1] This point of view is explained by the authors microbiologist Natália Pasternak and journalist Carlos Orsi.
[2] SNPs are genetic variations in a single base pair in the DNA sequence.
Resources: The Personalized Nutrition Study (POINTS): Evaluation of a genetically informed weight loss approach, 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.