Home › Nutrigenetics guide › Key nutrition genes

Nutrigenetics guide

The key genes for nutrition counseling

Reviewed by Dr. Daniel Wallerstorfer, molecular biologist and founder of Novogenia · Updated: 12 October 2026 · Reading time: 10 min

In short

For nutrition counseling, the most interesting genes are those whose effects are well researched: LCT (milk sugar), CYP1A2 (caffeine), MTHFR (folate), FTO (weight), FADS1/FADS2 (omega-3), VDR and GC (vitamin D), and PPARG, APOA2 and APOA5 (fat metabolism). For each gene, we show you what it does in the body, what research shows and what it means for your counseling. The recommendations that follow are logical conclusions – and together with measured values, they create a personal picture.

Same dose of caffeine, two results

101 male competitive athletes, a 10-kilometer cycling time trial, caffeine or placebo. With 4 mg of caffeine per kilogram of body weight, athletes with the AA genotype of CYP1A2 rode 6.8% faster. Those with CC were 13.7% slower on the same dose. With AC, nothing changed (Guest et al., Medicine & Science in Sports & Exercise 2018).

Caffeine is a double-edged sword – and which edge cuts depends partly on genes. Differences like these make nutrigenetics so exciting for your counseling. This article presents the genes you will meet most often.

On language: In plain-language passages, we speak of “functioning” or “effective” and “impaired” genes. This is a deliberate simplification – technically, we mean gene variants (polymorphisms). Where it helps, we also give the genotypes you will find in studies.

Our selection: lifestyle genes with a solid research base

This article covers only genes from the lifestyle and nutrition field. We present each gene in the same pattern:

What the gene does – its job in the body, explained with an everyday image.
What research shows – the key studies and their results.
What it means for counseling – the logical conclusion for your conversation.

The genes at a glance

Gene	What it does	What research shows	In counseling
LCT	controls whether lactase stays active in adulthood	C/T-13910 is closely linked to milk-sugar digestion	choose dairy products consciously
CYP1A2	breaks down caffeine; can be ramped up	AA breaks it down faster in smokers; in sport, AA carriers benefited from caffeine	amount and timing of caffeine
MTHFR	converts folate into its main circulating form	TT goes along with lower blood folate on average	folate-rich diet, include blood values
FTO	influences body weight	exercise weakens the effect; carriers lose weight just as well	motivation: the predisposition can be offset
FADS1/FADS2	convert plant omega-3 into EPA and DHA	variants are strongly linked to omega-3 levels in the blood	consider direct EPA/DHA sources
VDR / GC	docking site and transporter for vitamin D	GC, DHCR7 and CYP2R1 shape the vitamin D level	the vitamin D blood level sets the direction
PPARG	control center of fat-cell formation	Pro12Ala was associated with lower BMI and better insulin sensitivity	a building block for fat and carbohydrate sensitivity
APOA2	fat metabolism	CC: higher BMI only with a lot of saturated fat	with CC, watch saturated fat
APOA5	fat metabolism in the blood	influences triglycerides	have blood lipids assessed by a physician

LCT: the scissors for milk sugar

What the gene does: Lactase is the pair of scissors in the gut that cuts milk sugar into glucose and galactose. In many people, the body turns these scissors down after weaning – that is natural lactase non-persistence. In others, they stay in use for life.

What research shows: The C/T-13910 variant upstream of the LCT gene helps decide this: in Finnish families, it was completely associated with biochemically verified lactase non-persistence (Enattah et al., Nature Genetics 2002).

For counseling: With functioning lactase persistence, there is no genetic reason to avoid dairy. If the result points to non-persistence, it helps your client choose lactose-containing foods consciously – whether and at what amount complaints occur is individual. Persistent digestive complaints need a medical work-up. More in the gene story Lactose, calcium and the LCT gene.

CYP1A2: your tool against caffeine

What the gene does: CYP1A2 is your tool against caffeine – it breaks caffeine down. What makes it special: this tool can be ramped up, for example by smoking.

What research shows: The much-studied variant rs762551 helps determine how far the tool can be ramped up. Among smokers, people with the AA genotype broke down caffeine markedly faster than those with AC or CC (Sachse et al., British Journal of Clinical Pharmacology 1999). How practical this is shows in the cycling study above: AA carriers got faster with caffeine.

For counseling: It follows that with AA, caffeine before endurance efforts can make sense; with CC, there is a lot to be said for restraint – before competitions and in the evening. These are logical conclusions that you check against the person’s own experience. More in Caffeine and the CYP1A2 gene.

MTHFR: the folate workshop

What the gene does: MTHFR converts folate into 5-methyltetrahydrofolate, the main form of folate in the blood. Riboflavin (vitamin B2) is the helper this workshop needs.

What research shows: The 677C>T variant makes the workshop more heat-sensitive and less active (Frosst et al., Nature Genetics 1995). A meta-analysis in healthy women found 13% lower serum or plasma folate on average with two impaired gene copies (TT) than with two functioning ones (CC) (Tsang et al., American Journal of Clinical Nutrition 2015). And the helper makes a difference: in a randomized trial, the blood marker homocysteine fell by as much as 22% with riboflavin in people with TT – while there was no response in CC and CT (McNulty et al., Circulation 2006).

For counseling: With TT, a diet rich in folate and riboflavin is an obvious focus – with plenty of vegetables and legumes. Whether someone is well supplied is shown by diet and blood values. More in Folic acid and the MTHFR gene.

FTO: a headwind you can turn

What the gene does: FTO influences body weight – it harbors the strongest known genetic susceptibility locus for obesity (Kilpeläinen et al. 2011, see below).

What research shows: Adults with two unfavorable copies weighed about 3 kg more on average (Frayling et al., Science 2007). The good news: this headwind can be turned. In physically active adults, the effect of the FTO variant was 27% weaker (Kilpeläinen et al., PLoS Medicine 2011). And in eight randomized trials with 9,563 participants, carriers of the variant lost weight just as well as others in diet, exercise or drug-based programs (Livingstone et al., BMJ 2016).

For counseling: FTO is your best example of “genes are not destiny”. It follows that with an unfavorable FTO result, exercise deserves a firm place in the plan. More in Hunger, satiety and the FTO gene.

FADS1/FADS2: the omega-3 conversion line

What the genes do: Your body converts plant omega-3 (ALA, for example from flaxseed oil) into EPA and other long-chain omega-3 fatty acids. FADS1 and FADS2 are part of this conversion line.

What research shows: In a genome-wide meta-analysis of 8,866 people, carriers of certain FADS variants had more ALA and less EPA and DPA in their blood – their conversion line apparently runs slower (Lemaitre et al., PLoS Genetics 2011).

For counseling: It follows that with an impaired conversion line, it pays to focus on direct sources of EPA and DHA such as oily fish or algae oil instead of relying on ALA alone.

VDR and GC: lock and transporter for vitamin D

What the genes do: Vitamin D works like a key that fits a lock – the vitamin D receptor, built according to the instructions of the VDR gene. The GC gene provides the transporter that carries vitamin D in the blood to the cells.

What research shows: VDR variants have been studied intensively for years. Common markers such as BsmI, ApaI and TaqI probably stand in for functional variants nearby; such common variants can have subtle but real biological effects (Uitterlinden et al., Gene 2004). For the vitamin D level in the blood, a genome-wide study of 33,996 people found clear signals near GC, DHCR7 and CYP2R1: people in the least favorable quarter of a genetic score had 2.47-fold increased odds of a level below 75 nmol/L compared with the most favorable quarter (Wang et al., Lancet 2010).

For counseling: It follows that with unfavorable vitamin D genes, it is especially worthwhile to have the blood level measured and to adjust sun exposure, diet and, where appropriate, supplementation to it. The blood level sets the direction. More in Vitamin D and the VDR gene.

PPARG, APOA2, APOA5: fat, weight and blood lipids

PPARG – the control center of fat-cell formation: The Pro12Ala variant makes it less active and was associated with lower BMI and better insulin sensitivity in Finns (Deeb et al., Nature Genetics 1998). In counseling, PPARG is one building block that, together with other genes, creates a picture of fat and carbohydrate sensitivity.
APOA2 – a switch that flips with a lot of saturated fat: People with the CC genotype had a 6.2% higher BMI at 22 g or more of saturated fat per day, and no difference at lower intakes – confirmed in three independent populations (Corella et al., Archives of Internal Medicine 2009). It follows that with CC, a close look at saturated fat is especially worthwhile.
APOA5 – a regulator of blood lipids: APOA5 influences triglycerides in the blood (Pennacchio et al., Science 2001). Blood lipids are lab values; their assessment belongs with a physician.

How Novogenia describes fat and carbohydrate sensitivity is shown in the gene story Dietary fat sensitivity and your metabolism genes.

What does not belong in nutrition counseling

Some diet-related genes concern disease risks: HLA-DQ2/DQ8, HFE, APOE or thrombosis factors, plus pharmacogenetics. These are medical analyses. Where national law requires it, they belong in medical hands – even if a client asks about them.

Four sentences that help in conversation

“Your genes show a tendency – your measured values show how you are doing today.”
“This result is well supported. The recommendation based on it is a logical conclusion.”
“An unfavorable result shows you where your effort pays off most.”
“That question belongs with a physician – I’ll help you with your diet.”

How we do it at Novogenia

This is how we use these genes in our analyses:

Topics: The nutrition analysis shows, for example, how the body processes lactose, caffeine, vitamins, fats and carbohydrates, plus folate metabolism and iron and calcium absorption.
Three-study rule: A gene is only included if at least three independent studies support the effect; we do not report insufficiently documented variants.
Color code: Each report bundles several analyses around one part of everyday life, color-coded to the person’s genes – in up to 18 languages.
No gene, no dose: A statement like “gene X gives nutrient Y at dose Z” would be incorrect. Our algorithm for personalized supplements uses around 50 genes with three genotypes each, plus body data, a questionnaire and – where available – blood values. Blood values take precedence.

Frequently asked questions

Which genes are particularly well researched for nutrition counseling?

Particularly well researched are genes with a known mechanism and repeatedly confirmed effects: LCT for lactase persistence, MTHFR for folate metabolism, CYP1A2 for caffeine metabolism and FADS1/FADS2 for omega-3 levels in the blood. FTO is the best-known genetic factor for body weight – and a great example of how lifestyle can weaken a gene effect.

Does someone with the MTHFR TT genotype automatically need a special form of folate?

That cannot be derived from the genotype alone. On average, the TT genotype goes along with lower blood folate. Whether someone actually lacks folate is shown by their diet and blood values. Recommendations based on the genotype are logical conclusions; questions about blood values and disease belong with a physician.

Can someone with an unfavorable FTO result lose weight successfully?

Yes. A meta-analysis of 9,563 participants from eight randomized trials found that people with the unfavorable FTO variant respond just as well to diet, exercise or drug-based weight-loss programs as others. In physically active adults, the effect of the variant was also 27% weaker. So above all, the FTO result is one thing: motivation.

Does an LCT analysis replace a medical work-up of digestive complaints?

No. The LCT analysis shows whether the genes point to lactase persistence or non-persistence. It does not tell you whether complaints come from that – persistent digestive complaints need a medical work-up. In counseling, the result helps your client choose dairy products consciously.

Why are HFE, APOE or HLA-DQ not part of the nutrition analysis?

Because they are medical analyses: they concern disease risks, such as iron overload or a predisposition to celiac disease. Where national law requires it, such analyses belong in medical hands – with medical advice and interpretation. Nutrition counseling focuses on lifestyle topics.

Want to offer nutrigenetics in your practice?

Tell us about your practice and your clients – we will show you which partner model fits.

Become a partner →Offer for nutrition professionals

Note: This guide is general information for professionals and does not replace medical or legal advice. The genetic traits determined in a genetic analysis are well documented (each gene included is backed by at least three independent studies); recommendations on nutrition, micronutrients and lifestyle derived from them are logical conclusions, not scientifically proven. Regulations can change; errors and changes excepted.