Adults who carry certain genetic variants that raise their risk of obesity are more susceptible to increases in waist circumference when eating a diet high in total fat and saturated fats, according to a study in Ghana.
The study, “Interaction between Metabolic Genetic Risk Score and Dietary Fatty Acid Intake on Central Obesity in a Ghanaian Population,” was published in the journal Nutrients.
The prevalence of obesity in African countries varies widely, from 5.3% in Uganda to 45.7% in South Africa.
A study estimated that nearly 43% of adults, mostly women and urban dwellers, in Ghana were either overweight or obese.
The factors that influence obesity risk are complex, involving an interplay of environmental factors, lifestyle, and genetics. Studies in European populations have identified more than 100 specific gene spots linked to body mass index (BMI), but such studies are lacking for African populations.
In the new study, researchers from Saudi Arabia, the U.K., and Ghana assessed the impact of lifestyle and genetic factors on obesity-related traits in healthy Ghanaian adults (ages 25 to 60) from the Asante ethnic group.
Of the 302 participants, 126 were not obese and 176 were overweight/obese, as determined by their BMI.
Participants were asked about their physical activity, using the Physical Activity Questionnaire version 2. Weekly physical activity was calculated in metabolic equivalents (MET-minutes).
People with total physical activity scores of at least 600 MET-minutes/week were classified as active while participants with lower scores were considered inactive. Dietary intake was collected via the participants’ 24-hour recall, and then the data for three days (two weekdays and one weekend day) was analyzed.
The genetic risk for obesity, calculated as genetic risk scores, was based on the analysis of DNA from blood samples. The researchers analyzed 12 small genetic variations, known as single nucleotide polymorphisms (SNPs), in eight genes linked to obesity in previous studies.
Obesity-related traits included BMI, waist circumference, waist-to-hip ratio, and percentages of body and visceral fat.
The analysis revealed that overweight and obese participants were significantly older than the non-obese. Also, the dietary intake between the two groups was significantly different: overweight or obese individuals reported significantly lower intakes of total calories, protein, carbohydrates, total fat, fiber, and several fatty acids, including saturated fatty acids (SFA), monounsaturated (MUFA), and polyunsaturated fatty acids (PUFA).
Despite consuming less carbohydrate, protein, and fat than men, women had a significantly higher percentage of body fat, BMI, and waist-to-hip ratio.
The researchers found no association between the combined effect of all 12 SNPs and obesity-related traits.
They then performed a more restricted analysis excluding four SNPs due to their very low frequency, and an even more stringent analysis with four SNPs — located in the TCF7L2, MC4R, and FTO genes — that excluded mutations poorly associated with obesity-related traits in other populations.
Among adults with higher intake of total fat (above 47 grams/day), individuals with three or more risk alleles (gene copies) of the six in the restricted group of four SNPs had higher waist circumference than participants with fewer risk alleles.
The link was maintained for fatty acids — above 14 grams/day for SFA, and above 16 grams/day each for MUFA and PUFA. Diets rich in SFA, like those found in fatty meats, increase the risk of heart disease. In contrast, unsaturated fats are perceived as good fats.
Body fat was also significantly greater among adults with a higher intake of fiber (above 19 grams/day) and who carried three or more risk alleles.
Overall, “our study has shown that higher intakes of total fat, SFA, MUFA and PUFA can increase the genetic risk on [waist circumference] in Ghanaian adults,” the researchers wrote.
“These results support the general dietary recommendations to decrease the intakes of total fat and SFA, to reduce the risk of obesity, particularly in individuals with a higher genetic predisposition to central obesity,” they concluded.
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