Increasing nut consumption by just half a serving (14g or half an ounce) a day is linked to less weight gain and a lower risk of obesity, suggests a large, long-term observational study, published on Sept 23, 2019, in the online journal BMJ Nutrition, Prevention & Health.
Substituting unhealthy foods such as processed meats, french fries and potato chips with a half a serving of nuts may be a simple strategy to ward off the gradual weight gain that often accompanies the ageing process, suggest the researchers.
On average, American adults pile on one pound or nearly half a kilogramme every year. Gaining 2.5kg to 10kg in weight is linked to a significantly greater risk of heart disease, stroke and diabetes.
Nuts are rich in healthy unsaturated fats, vitamins, minerals and fibre, but they are calorie-dense, and therefore not often thought good for weight control. But emerging evidence suggests that the quality of what’s eaten may be as important as the quantity.
Amid modest increases in ave-rage nut consumption in the United States over the past two decades, the researchers wanted to find out if these changes might affect weight control.
They analysed information on weight, diet and physical activity in three groups of people: 51,529 male health professionals aged 40 to 75 enrolled in the Health Professionals Follow Up Study; 121,700 nurses aged 35 to 55 in the Nurses Health Study (NHS); and 116,686 nurses aged 24 to 44 in the Nurses Health Study II (NHS II).
Over more than 20 years of monitoring, participants were asked every four years to state their weight, and how often, over the preceding year, they had eaten a serving (28g or 1oz) of nuts, including peanuts and peanut butter.
Average weekly exercise – walking, jogging, cycling, swimming, racquet sports and gardening – was assessed every two years by questionnaire. It was measured in metabolic equivalent of task (MET) hours, which express how much energy (calories) is expended per hour of physical activity.
Average annual weight gain across all three groups was 0.32kg.
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.
Increasing consumption of any type of nut was associated with overall less long-term weight gain and a lower risk of becoming obese (defined as a BMI of 30 or more). Increasing nut consumption by half a serving a day was associated with a lower risk of putting on two or more kilogrammes over any four-year period.
A daily half-serving increase in walnut consumption was associated with a 15% lower risk of obesity.
Substituting processed meats, refined grains or desserts, including chocolates, pastries, pies and doughnuts, for half a serving of nuts was associated with staving off weight gain of between 0.41kg and 0.70kg in any four-year period.
Within any four-year period, upping daily nut consumption from none to at least half a serving was associated with staving off 0.74kg in weight, a lower risk of moderate weight gain and a 16% lower risk of obesity, compared with not eating any nuts.
And a consistently higher nut intake of at least half a serving a day was associated with a 23% lower risk of putting on five or more kilogrammes and of becoming obese over the same timeframe.
No such associations were observed for increases in peanut butter intake. The findings held true after taking account of changes in diet and lifestyle, such as exercise and alcohol intake.
However, the data relied on personal report, which may have affected accuracy, while only white, relatively affluent health professionals were included, so the findings may not be more widely applicable.
But the findings echo those of previous observational studies, note the researchers, who attempt to explain the associations they found.
They suggest that as chewing nuts takes some effort, it leaves less energy for eating other things, while the high fibre content of nuts can delay stomach emptying, making a person feel sated and full for longer.
Nut fibre also binds well to fats in the gut, meaning that more calories are excreted. And there is some evidence that the high unsaturated fat content of nuts increases resting energy expenditure, which may also help to stave off weight gain.
Snacking on a handful of nuts, rather than biscuits or potato chips. may help to ward off the weight gain that often accompanies ageing and is a relatively manageable way of helping to curb the onset of obesity, they suggest. And a nut habit is likely to be good for the planet, they add.
“In addition to the impact on human health, using environmentally-friendly plant-based protein, such as nuts and seeds, to replace animal sources of protein may contribute to the promotion of a global sustainable food system,” they write.