In a large multi-year study, investigators study the benefits of eating nuts in preventing gradual weight gain.
Despite being high in calories, just a half serving of nuts per day (14 gm or ½ oz) is associated with a lower risk of weight gain and obesity, just one of the benefits of eating nuts, according to a study published by the BMJ Nutrition, Prevention & Health.
On average, adults in the U.S. accumulate around half a kilogram of weight per year throughout adulthood. Even modest weight gain (2.5-10 kg) in adulthood increases mortality and subsequent risk of having diabetes, stroke, and obesity-related cancer. Prevention of weight gain over time may be an effective measure to prevent lifestyle diseases.
Establishing healthy dietary patterns, rather than a singular focus on total calories, may be a positive lifestyle intervention that supports weight management. The high-fat content of nuts is associated with perceptions that they are unhealthy and should be avoided by those attempting to lose weight.
Amid modest increases in average nut consumption in the U.S. over the past two decades, researchers from Harvard University wanted to determine if these changes might affect weight control.
They analyzed information on weight, diet, and physical activity in three groups of people: 51,529 male health professionals, aged 40 to 75 when enrolled in the Health Professionals Follow Up Study; 121,700 nurses, aged 35 to 55 when recruited to the Nurses Health Study (NHS); and 116,686 nurses, aged 24 to 44 when enrolled in the Nurses Health Study II (NHS II).
These researchers investigated the association between changes in nut consumption over four-year intervals and concurrent weight change. The researchers assessed the participants’ – dietary patterns, weight change, and physical activity (e.g., walking, jogging, bicycling, swimming, racquet sports, and gardening) – periodically by questionnaires. They measured the physical activity in metabolic equivalent of task (MET) hours, which express how much energy (calories) is expended per hour of physical activity.
The average annual weight gain across all three groups was 0.32 kg (0.71 lb). Between 1986 and 2010. Total nut consumption rose from a quarter to just under half a serving per day in men, and from 0.15 to 0.31 servings per day among the women in the NHS study. Between 1991 and 2011, total daily nut consumption rose from 0.07 to 0.31 servings among women in the NHS II study.
Overall, increasing consumption of any nut was associated with less long-term weight gain and a lower risk of becoming obese.
Increasing nut consumption by half a serving a day was associated with a lower risk of gaining around two or more kilos over any four-year period. A daily, half serving increase in walnut consumption was associated with a 15% lower risk of obesity. Increasing peanut consumption was not related to the risk of obesity.
Within any four years, upping daily nut consumption from none to at least half a serving was associated with a lesser weight gain of 0.74 kg, a lower risk of moderate weight gain, and a 16% lower risk of obesity, compared with not eating any nuts.
The findings held after taking into account changes in diet and lifestyle, such as exercise and alcohol intake.
Why are there benefits to eating nuts?
The researchers suggest that chewing nuts require energy. The high fibre content of nuts can delay gastric emptying, increase satiety, suppress hunger, and the desire to eat and promote fullness. The nut fibre binds well to fats in the gut, meaning that more calories are excreted.
There is also evidence that the unsaturated fat composition of nuts elevates the resting energy expenditure, which may contribute to the mitigation of weight gain.
Snacking on a handful of nuts rather than muffins or potato crisps may help to ward off the weight gain that often accompanies aging and is a realistic and attainable dietary modification to curb the onset of obesity, the researchers suggest.
It is important to note that the study is observational in nature, and as such, can’t establish a cause-effect relationship. Furthermore, the data relied on the personal report of participants, which may have affected accuracy to some extent. Simultaneously, only white, relatively affluent health professionals were included, so the findings may not be more widely applicable. Further research is therefore necessary to assess the generalisability of the results.
Xiaoran Liu , Yanping Li, Marta Guasch-Ferré, Walter C Willett, Jean-Philippe Drouin-Chartier, Shilpa N Bhupathiraju, Deirdre K Tobias. Changes in nut consumption influence long-term weight change in US men and women. BMJ Nutrition, Prevention & Health. 2019; 2:90–99. doi:10.1136/bmjnph-2019-000034.
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