Potato chips, other potatoes, sugary drinks, processed and unprocessed meat were found to be the foods most strongly linked to creeping weight gain, according to an analysis of studies that followed over 120,000 adults for 20 years. The researchers said their evidence supports the idea that "eat less and exercise more" may be too simplistic a weight-loss strategy. It is the quality of food that matters most and making a handful of small, targeted changes is likely to be more effective.
The researchers, from the Harvard School of Public Health (HSPH) in Boston, Massachusetts, write about their findings in the 23 June online issue of the New England Journal of Medicine, NEJM.
Senior author Dr Frank Hu, professor of nutrition and epidemiology at HSPH, told the press their findings:
"... underscore the importance of making wise food choices in preventing weight gain and obesity."
"The idea that there are no 'good' or 'bad' foods is a myth that needs to be debunked," he added.
Many studies focus on what to do after people become overweight or obese, and we know less about what lies behind the creeping weight gain that happens over one or two decades.
Lead author Dr Dariush Mozaffarian, an associate professor in the Department of Epidemiology at HSPH, said:
"An average adult gains about one pound per year. Because the weight gain is so gradual and occurs over many years, it has been difficult for scientists and for individuals themselves to understand the specific factors that may be responsible."
Mozaffarian, who is also a professor in HSPH's Division of Cardiovascular Medicine, Brigham and Women's Hospital (BWH), and Harvard Medical School, and colleagues conducted three separate prospective analyses to look at how changes in diet and lifestyle linked to long term weight gain.
They found that small changes in diet, consumption of beverages, physical activity, watching TV, and sleep duration were the factors most strongly linked to long-term weight gain, and the strongest of these, was changes in diet.
They analyzed data from participants taking part in three separate large scale long term studies: the Nurses' Health Study (NHS: 50,422 women included in their final analysis), the Nurses' Health Study II (NHS II: 47,898 women included), and the Health Professionals Follow-up Study (HPFS: 22,557 men included). These studies followed participants from 1986 to 2006, 1991 to 2003, and 1986 to 2006, respectively.
All of the participants were free of obesity and chronic diseases at the start of the study period.
Mozaffarian and colleagues expressed their results according to 4-year intervals and over 20 years. For each 4-year interval, they found that the average weight gain per participant was 3.35 lbs (1.52 kg), which corresponds to an average of 16.8 lbs (7.62 kg) over 20 years.
When they looked at links between lifestyle changes and weight gain, they found very similar results across the three cohorts. Increases in daily servings of foods such as potatoes, sugary drinks and meats contributed significantly to the average weight gain, whereas increases in daily servings of foods such as vegetables, whole grains, fruits and nuts, tended to work in the other direction.
For instance, on the basis of increased daily servings of individual dietary components, the following foods were linked to increased weight gain:
Potato chips ("crisps" in the UK) accounted for +1.69 lbs of the 3.35 lbs average weight gain every 4 years.
Other potatoes accounted for +1.28 lbs.
Sugary drinks: +1.00 lbs.
Unprocessed meats: +0.95 lbs.
Processed meats: +0.93 lbs.
On the other hand, the impact of the following foods was linked to less weight gain when people gradually ate more of them:
Vegetables: accounted for -0.22 lbs (ie a reduction) in the 3.35 lbs average weight gain every 4 years.
Whole grains accounted for -0.37 lbs.
Fruits: -0.49 lbs.
Nuts: -0.57 lbs.
Yogurt: -0.82 lbs.
Mozaffarian and colleagues also found that changes in lifestyle habits, such as reduced levels of physical activity and more hours spent in front of the TV also linked to increase in weight. Hours of sleep also appears to play a role, with those who slept 6 to 8 hours gaining less weight than those who slept less than 6 hours or more than 8 hours a night.
However, while the amount of weight gain linked to any one lifestyle change was small, it was their total effect that made the difference. A cluster of lifestyle changes can make a significant impact, for "bad or good", said Mozaffarian.
"This makes it easy to gain weight unintentionally, but also demonstrates the tremendous opportunity for prevention. A handful of the right lifestyle changes will go a long way," he added.
The researchers suggest their findings show it is not a good idea to focus on total calories as a way to lose weight. Even other measures such as total fat, energy density, and sugar content could also be misleading.
We would do better, they say, if we attend to the overall quality of our diet, and focus on improving carbohydrate quality, consuming less processed foods and increasing our intake of minimimally processed foods: in other words:
Less sugary liquids, such as sodas.
Fewer potatoes and refined grains like white bread, white rice, low-fiber breakfast cereals.
Less processed meats.
More fruits, vegetables, whole grains, nuts and yogurt.
They also suggest that moving to a more healthful dietary pattern changes our biological process of weight gain in the longer term. This works through changes in hunger thresholds, insulin, and feeling of fulness.
Funds from the National Institutes of Health and the Searle Scholars Program helped pay for the study.