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https://doi.org/10.1136/bmj-2022-073939
Disclaimer: This article contains descriptions of weight gain and dieting
Introduction:
Obesity continues to increase globally, with a majority of the US population being affected. Diets with varying macronutrient compositions are widely promoted, but weight loss trials have not directly dealt with the leading cause of obesity: small, gradual weight gain in midlife. Low-fat and low-carbohydrate diets are suggested to be an advantage for weight loss, but it has been proven through randomised trials that low-fat diets have more of an impact on weight loss than low-carbohydrate diets. This study suggested that weight changes would be stronger in people who are already overweight or obese, as they are predisposed to weight gain.
Previous Research:
Rather than the intake of carbohydrates itself, there may be a role of quality and source of carbohydrates with weight control. For instance, higher intakes of whole grains and dietary fibre are correlated with weight loss, but refined grains have been associated with weight gain. It is recommended by dietary authorities such as The Dietary Guidelines for Americans that half one’s intake of grains should be whole grains; all intake of vegetables (including starchy vegetables) should be increased, and all added sugars should be limited to less than 10% of the daily energy intake. However, most observational studies of carbohydrate intake and body weight have been limited by the fact that they all assigned one specific diet to all participants, so long-term weight gain appeared constant. Due to these factors, this study investigated alterations in carbohydrate quality and quantity with weight change among men and women with 4-year intervals.
Summary:
There were over 100,000 participants in this study, all aged 65 or younger and free of any conditions (diabetes, cancer, cardiovascular disease etc) that could interfere with the results of the study. The diet was assessed using questionnaires, accounting for total carbohydrate intake as well as participants’ typical intakes of other nutrients, such as fibre, starch, added sugars and natural sugars as well as major foods, such as whole grains, refined grains, fruits, and vegetables. The outcome of the weight change was completed by self-reported numbers. The participants updated information on physical activity, smoking status, sleep duration, hours of sitting and watching television, and other factors that affect weight.
Analyses for changes in body mass index (BMI) were also conducted in the same four-year period and the effects of substitutions of carbohydrates, such as alternative flours, as well. The primary form of measurement of changes in these foods was the glycemic index. The glycemic index is a measurement of how quickly a food can make one’s blood glucose rise. This was used because only foods with a carbohydrate content tend to have a glycemic index.
Conclusion:
On average, participants gained about 1.5 kilograms every 4 years. In both men and women, an increased glycemic index was associated with weight gain. Foods such as added sugar and starch were directly associated with weight gain. As participants increased their intake of starch and added sugar by 100 grams per day, their weight gain over 4 years was greater than the average of 1.5 kilograms. On the other hand, non-starchy vegetables had a lower association with weight gain. Many of these associations were stronger in women. A major strength of this study was its large sample size, which allowed for a more reliable comparison. Moreover, there were repeated questionnaires and dietary assessments that enabled the researchers to conduct close studies of the participants. In addition to the quantity of carbohydrates consumed, the study also placed a focus on aspects of the quality of carbohydrates being consumed. However, a major limitation was that there was a dependence on self-reported questionnaires and assessments, which may not have been reliable if participants underreported their BMIs on a given trial. Taking these factors into account, the study did highlight the importance of the source and quality of carbohydrate intake on weight management in the long term, especially for overweight or obese people. In conclusion, limiting added sugar, refined grains and starchy vegetables in favour of whole grains, fruit and non-starchy vegetables may support weight control.
Sources:
Wan, Yi, et al. “Association between Changes in Carbohydrate Intake and Long Term Weight Changes: Prospective Cohort Study.” BMJ, vol. 382, 27 Sept. 2023, p. e073939, www.bmj.com/content/382/bmj-2022-073939, https://doi.org/10.1136/bmj-2022-073939. Accessed 28 Sept. 2023.
CDC. “Notice of Funding Opportunity: HOP.” Centers for Disease Control and Prevention, 1 Feb. 2023, www.cdc.gov/nccdphp/dnpao/state-local-programs/fundingopp/2023/hop.html#:~:text=Obesity%20in%20the%20United%20States.
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