Just a few more grams of daily fiber could help millions of Americans prevent obesity and live longer. But how much do you need for maximum protection?
Study: Association between dietary fiber intake and obesity in US adults: from NHANES 1999–2018. Image credit: marilyn barbone/Shutterstock.com
A recent study in Frontiers in Nutrition investigated the effects of dietary fiber intake on American adults with obesity and found that higher dietary fiber intake was associated with a significantly lower risk of obesity among adults, though causation cannot be proven.
Obesity and health risks
Obesity is a medical condition characterized by the accumulation of excessive body fat. It is a metabolic condition that affects individuals of all ages, which increases the risk of incidence of various diseases, including cancer, diabetes, and cardiovascular disease.
In 2022, the World Health Organization estimated that more than 2.5 billion adults worldwide were overweight, among whom approximately 890 million were obese. Therefore, effective interventions are urgently needed to alleviate this global obesity problem.
Multiple studies have demonstrated the effectiveness of various dietary interventions, including low-carbohydrate, Mediterranean, and vegetarian diets, in achieving effective weight management. A combination of nutritional interventions and physical activity has been recommended for the treatment of obesity.
Among many nutritional components, dietary fiber significantly regulates blood glucose and lipid levels, maintains intestinal health, and promotes intestinal motility. According to the 2020–2025 dietary guidelines, individuals under 51 have been recommended a daily intake of 25 and 38 grams of dietary fiber for women and men, respectively. Among individuals aged 51 years and above, men should intake 30 grams daily, and women should target 21 grams.
It is worth noting that most American adults do not meet these recommended levels. Specifically, about 97% of men and 90% of women fall short of the suggested intake. The insufficient intake of dietary fiber increases the risk of otherwise preventable obesity-related complications, such as hyperlipidemia, diabetes, metabolic syndrome, and coronary heart disease.
Research has also shown that increased fiber intake is linked with lower mortality from all causes and cardiovascular disease, although this relationship has not been observed for cancer mortality. It is essential to determine whether consuming adequate dietary fiber reduces obesity-related consequences. This information will help scientists to develop effective diet-based interventions to reduce obesity and its associated risks.
About the study
The current study hypothesized that dietary fiber intake is inversely associated with the incidence of obesity and that increased dietary fiber intake can reduce the all-cause mortality risk in obese individuals. To test this hypothesis, the National Health and Nutrition Examination Survey (NHANES) database (1999–2018) was used.
The NHANES provides comprehensive US-based data on health and nutrition managed by the National Center for Health Statistics. It also offers other information, such as socio-economic status, demographics, health issues, physiological measurements, and laboratory test results.
In the first part of the study, 101,316 participants were screened, and those below 18 years of age, pregnant individuals, and those with missing data were excluded from the cohort. A total of 39,184 participants fulfilled the eligibility criteria and were considered to assess the cross-sectional correlation between dietary fiber intake and obesity.
To assess the longitudinal relationship between mortality and dietary fiber intake among obese patients, 14,421 eligible adults with a body mass index (BMI) of 30 kg/m² or higher were included. The median follow-up duration was 9.08 years.
The study adjusted for a wide range of confounding factors, including age, gender, ethnicity, education, income, marital status, energy intake and physical activity, comorbidities, and health behaviours like smoking and alcohol consumption.
Study findings
At baseline, participants were divided into obese and non-obese groups. The obese group comprised 14,436 participants, while the non-obese group comprised 24,748. The mean age of the participants in the non-obese group was 46.60 years, and the mean dietary fiber intake was 17.11 grams per day. In contrast, the mean age of the obese participants was 48.15 years, and the mean dietary fiber intake was 15.80 grams per day.
A marginally higher proportion of the cohort was female, and 70.51% were non-Hispanic White. Approximately 70% of the cohort had a high level of education, and 36% had a poverty income ratio (PIR) level greater than 3.0. The majority of the study cohort was married or cohabiting and consumed alcohol, while 46.84% were smokers. Some participants also had a history of diabetes and hypertension.
Multifactorial logistic regression analysis indicated a negative correlation between dietary fiber and obesity. This finding suggests that increased dietary fiber consumption may lower the risk of obesity. Fully adjusted models also showed that dietary fiber intake was negatively correlated with obesity.
An intake greater than 20.8 grams of dietary fiber per day corresponded to the highest protective effect, with the lowest risk of obesity. Restricted cubic spline (RCS) curve analysis stratified by alcohol consumption status indicated that obese non-drinkers, non-Hispanic Black, and non-smoking populations benefited more with increasing dietary fiber intake compared to drinkers, smokers, and Hispanic groups.
The multivariable-adjusted spline regression model revealed a non-linear, U-shaped association between dietary fiber intake and all-cause mortality, with 26.3 grams per day as the intake level associated with the lowest risk of death among obese participants.
A stratified weighted multiple regression analysis indicated a consistent negative correlation between dietary fiber intake and obesity incidence across different lifestyles, demographic characteristics, and disease statuses. Similarly, the subgroup analysis showed a negative correlation between fiber consumption and all-cause mortality across different lifestyles, demographic characteristics, and disease statuses.
However, the study did not find a statistically significant association between dietary fiber intake and lower cancer mortality among obese individuals. For cardiac mortality, results were less consistent across all statistical models.
The authors note that while these associations are compelling, the study’s cross-sectional and observational design cannot establish causality, meaning it cannot prove that higher fiber intake directly causes lower obesity or mortality risk.
The study also discusses possible mechanisms by which dietary fiber could help prevent obesity, such as promoting satiety, delaying gastric emptying, regulating gut hormones, and improving insulin sensitivity and inflammation.
Conclusions
The current study emphasized that increased dietary fiber intake could significantly lower the risk of obesity incidence and all-cause mortality in the obese population. The lowest all-cause mortality among obese adults was seen at a fiber intake of 26.3 grams per day, though even modest increases above current average intakes were linked to benefit.
Therefore, a fiber-rich diet should be further investigated as a potential dietary intervention to treat obesity. The findings support current public health guidelines, but the authors caution that further longitudinal and intervention studies are needed to confirm the results.
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