What you carry at this position in your DNA and what research says about it.
Obesity Risk: 8/10 evidence, 40 publications.
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Sample genotype (not yours): T/T
Typical Obesity Risk but Slightly Higher Breast Cancer Risk
This genotype is associated with a typical body mass index and lower risk of obesity. However, it carries a slightly increased risk for breast cancer and metabolic syndrome.
What this genotype means: Typical obesity risk; Slightly higher breast cancer risk; Slightly higher metabolic syndrome risk.
Sample genotype (not yours): G/G
Higher Obesity Risk but Lower Breast Cancer Risk
Carrying two copies of the G allele is associated with a higher risk of obesity and non-alcoholic fatty liver disease. Conversely, it is linked to a lower risk of breast cancer.
What this genotype means: Higher obesity risk; Lower breast cancer risk; Higher fatty liver risk.
Sample genotype (not yours): T/G
Moderately Increased Obesity Risk
Carrying one copy of the G allele is linked to a moderately higher risk of obesity and weight gain. It also correlates with slightly higher blood sugar levels.
What this genotype means: Moderately increased obesity risk; Typical breast cancer risk; Typical metabolic syndrome risk.
Gene function and biological role
Gene Function: FTO encodes an enzyme that plays a key role in energy homeostasis and nucleic acid demethylation [1]. It is highly expressed in the hypothalamus, a brain region that regulates appetite and satiety [2]. Variations in this gene are among the most well-established genetic contributors to common obesity in humans [3]. Research suggests that FTO influences how the body processes energy and regulates food intake [4]. Despite these genetic influences, lifestyle factors like diet and exercise remain powerful tools for managing weight [5].
Variant Impact: rs17817449 is an intron variant in the FTO gene that is in strong linkage disequilibrium with other key obesity-associated variants like rs9939609 [6]. The G allele of this variant is associated with increased body mass index (BMI) and obesity risk across diverse populations [3]. Conversely, the T allele is associated with a slightly higher risk of breast cancer [7]. This variant represents a classic genetic trade-off between metabolic traits and oncological risks [1]. Understanding this variant helps tailor metabolic and lifestyle strategies for optimal health [5].
Key Insight: This variant represents a genetic trade-off where the allele that increases obesity risk actually lowers breast cancer risk, and vice versa.
Location: FTO. Chromosome 16 · 16q12.2 · 53.8 Mb
Estimated prevalence by population
Global 38.3%; European 35.0%; African 36.7%; East Asian 71.9%; South Asian 46.9%; Americas 48.1%; Ashkenazi 24.5%; Finnish 36.1%; Middle Eastern 37.9%; Amish 28.9%.
Estimated TT genotype frequency.
Global 46.6%; European 48.3%; African 47.8%; East Asian 25.8%; South Asian 43.2%; Americas 42.5%; Ashkenazi 50.0%; Finnish 48.0%; Middle Eastern 47.3%; Amish 49.7%.
Estimated TG genotype frequency.
Global 15.1%; European 16.6%; African 15.6%; East Asian 2.3%; South Asian 9.9%; Americas 9.4%; Ashkenazi 25.5%; Finnish 15.9%; Middle Eastern 14.8%; Amish 21.4%.
Estimated GG genotype frequency.
Showing effects for T/T genotype
Cardiovascular & Metabolic
Obesity & Body Composition
Obesity. Evidence: 5/10. Source: PMID 21919686. Typical Risk.
Metabolic Syndrome & Insulin Resistance
Metabolic Syndrome. Evidence: 6/10. Source: PMID 38201907. Slightly Higher Risk.
Diabetes & Glycemic Traits
Blood Glucose. Evidence: 6/10. Source: PMID 33462484. Slightly Lower HbA1c.
Lipids & Cholesterol
HDL Cholesterol. Evidence: 6/10. Source: PMID 33462484. Slightly Higher HDL.
Cancer & Oncology
Breast Cancer
Breast Cancer. Evidence: 8/10. Source: PMID 27117709. Slightly Higher Risk.
Organ Systems
Liver Function & Disease
Fatty Liver Disease. Evidence: 6/10. Source: PMID 37709864. Slightly Lower Risk.
Showing effects for G/G genotype
Obesity. Evidence: 5/10. Source: PMID 21919686. ~1.7x Risk.
Metabolic Syndrome. Evidence: 6/10. Source: PMID 38201907. Slightly Lower Risk.
Blood Glucose. Evidence: 6/10. Source: PMID 33462484. Slightly Higher HbA1c.
HDL Cholesterol. Evidence: 6/10. Source: PMID 33462484. Slightly Lower HDL.
Breast Cancer. Evidence: 8/10. Source: PMID 27117709. Slightly Lower Risk.
Fatty Liver Disease. Evidence: 6/10. Source: PMID 37709864. Slightly Higher Risk.
Showing effects for T/G genotype
Obesity. Evidence: 5/10. Source: PMID 21919686. ~1.3x Risk.
Metabolic Syndrome. Evidence: 6/10. Source: PMID 38201907. Typical Risk.
Blood Glucose. Evidence: 6/10. Source: PMID 33462484. Typical Levels.
HDL Cholesterol. Evidence: 6/10. Source: PMID 33462484. Typical Levels.
Breast Cancer. Evidence: 8/10. Source: PMID 27117709. Typical Risk.
Fatty Liver Disease. Evidence: 6/10. Source: PMID 37709864. Typical Risk.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
The T/T genotype represents the baseline or normal genetic state for weight-related traits in the FTO gene region [1]. Clinical studies show that individuals with these alleles generally have a lower body mass index and a reduced likelihood of developing obesity compared to G allele carriers [2]. Large-scale genetic analyses have revealed a trade-off, showing that the T allele is associated with a slightly higher risk of breast cancer, particularly estrogen-receptor-negative subtypes [3]. Metabolic syndrome risk is also slightly elevated with this genotype [4]. Fortunately, maintaining a balanced diet and regular physical activity remains highly effective for overall metabolic health [5]. Research indicates that cardiovascular parameters and lipid profiles are generally favorable in this group [6]. Overall, this genetic profile highlights the complex balance between metabolic efficiency and other systemic health risks [7].
Typical obesity risk; Slightly higher breast cancer risk; Slightly higher metabolic syndrome risk.
Sample genotype: GG (Homozygous)
The G/G genotype is associated with a significantly higher risk of obesity, estimated at approximately 1.7-fold higher than the baseline [1]. This variant is associated with higher body mass index, larger waist circumference, and elevated fasting insulin levels [2]. It is also linked to an increased risk of non-alcoholic fatty liver disease and higher HbA1c levels [3]. However, this genotype is protective against breast cancer, showing a lower risk compared to T allele carriers [4]. It is also associated with a lower risk of metabolic syndrome [5]. Studies emphasize that intensive lifestyle interventions, including physical activity and dietary changes, can successfully counteract the genetic tendency toward weight gain [6]. Proactive health habits are particularly powerful for individuals with this genetic profile [7].
Higher obesity risk; Lower breast cancer risk; Higher fatty liver risk.
Sample genotype: TG (Heterozygous)
The presence of one G allele is associated with a moderate increase in body mass index and a roughly 1.3-fold higher risk of obesity [1]. This genetic influence is thought to affect appetite regulation, leading to a preference for more calorie-dense foods [2]. Research indicates that lifestyle interventions, such as regular exercise and dietary adjustments, are highly effective at mitigating this genetic predisposition [3]. On the positive side, carriers of the G allele have a slightly lower risk of developing breast cancer compared to those with the TT genotype [4]. They also show a reduced risk of metabolic syndrome [5]. Overall, this genotype represents a common genetic variation where daily habits play a crucial role in determining long-term health outcomes [6]. Active management of diet and exercise can completely offset the moderate genetic risk of weight gain [7].
Moderately increased obesity risk; Typical breast cancer risk; Typical metabolic syndrome risk.
Variants with shared genetic architecture
rs11075995 · FTO Gene · Chr 16 · Breast Cancer Risk
rs11642015 · FTO Gene · Chr 16 · Weight and Diabetes Risk
rs1421085 · FTO Gene · Chr 16 · Obesity and Weight Gain
The FTO gene is associated with adulthood obesity in the Mexican population.
FTO and MC4R gene variants determine BMI changes in children after intensive lifestyle intervention.
Identification of four novel susceptibility loci for oestrogen receptor negative breast cancer.
A Genome-Wide Association Study of Metabolic Syndrome in the Taiwanese Population.
Genetics of 35 blood and urine biomarkers in the UK Biobank.
Genomic analysis of diet composition finds novel loci and associations with health and lifestyle.
Content updated August 2026.
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