Genetics as a Nutrition Input: Nutrigenetics Evidence

Field, test and product: three different things

• The field: nutrigenetics, a branch of personalised nutrition research. [1]
• The test: a DNA test that reports which variants a person carries. Different direct-to-consumer genetic test companies do not test for the same set of variants and may give different results for the same condition. [3]
• The product: a diet or supplement report sold on the basis of a test. Commercial offerings in this area are often built on direct-to-consumer tests that are unregulated and have limited published evidence of benefit. [1]

A study finding for one gene and one food does not validate a report that bundles many genes. For basic genome terms, see Genomics Explained. For genes and medicines, see Pharmacogenomics, which is a separate topic.

What research shows

Observational gene-diet findings (promising but limited). In the Nurses' Health Study and Health Professionals Follow-up Study (6,934 women and 4,423 men), the genetic association with body mass index appeared stronger among people who drank more sugar-sweetened beverages, with a replication in 21,740 women. [4] This is an association in cohorts. It does not show that a person with a high genetic score would lose weight by changing the drink, and it does not reveal a personal prescription.

Randomized trial of genotype-based diet choice (no benefit found). The DIETFITS trial enrolled 609 adults with a body mass index between 28 and 40 and tested whether three genotype patterns matched them to a low-fat or low-carbohydrate diet. Weight change at 12 months was -5.3 kg and -6.0 kg, and there was no significant diet-genotype interaction. [5] The authors concluded that neither genetic pattern was helpful in identifying which diet was better for whom. [5]

Genes in prediction models. In the PREDICT 1 study, genetic variants had a modest impact on predicting responses: 9.5% for glucose, 0.8% for triglyceride and 0.2% for C-peptide. [6]

Does genetic advice change behavior? (mixed to no effect). A meta-analysis of 14 reports from 11 randomized studies found that genotype-based advice did not change dietary or physical activity behavior more than general advice or advice based on lifestyle or phenotype. [2] Evidence quality for the dietary outcome was low. [2] In Food4Me, the people who benefited most from personalised advice did not differ by genotype. [7]

Does it feel more useful? (a different question). In a small randomized survey study of 149 young adults, people given genotype-based advice found it more understandable and more useful than general advice. [8] Finding advice interesting is not the same as eating differently or being healthier.

Where to go next

For the consumer product claims, see DNA-Based Diets: What Trials Show. For everyday food guidance that applies without a test, see Food-First Nutrition.