Diet, lifestyle and long-term weight gain

Behind the Headlines

Thursday June 23 2011

“A simple way for people to stay slim without counting the calories has been discovered,” the Daily Express reported. It said that research suggested that instead of worrying about the amount of food we eat, we should concentrate on its quality. It continued that eating more ‘natural’ foods like fruit, vegetables and nuts is the best way to stay a healthy weight.

The story comes from a large study in nearly 121,000 people in the US that investigated dietary and lifestyle factors in relation to long-term weight gain.

Weight gain was found to be associated with eating crisps, potatoes, sugary drinks and processed meats but was less likely if people ate more vegetables, whole grains, fruits, nuts and yoghurt, with these foods associated with less weight gain when more was consumed.

This large study supports current advice to eat healthier foods such as fruit and vegetables and less fatty, sugary foods, to achieve a healthy weight in the long term. It also supports the idea that for most people trying to achieve a healthy weight, it is better to eat a healthy balanced diet rather than fixating on calorie counting.

However, the study does have some limitations and does not show that specific foods such as nuts will actually make you lose weight, regardless of calories consumed, as the study did not measure calories. It is also likely that people who eat healthier foods reduce their intake of other, higher calorie foods, and so have fewer calories to burn off.

 

Where did the story come from?

The study was carried out by researchers from Brigham and Women’s Hospital and Harvard medical school and the Harvard School of Public Health, all in Boston. It was funded by the National Institutes of Health and the Searle Scholars Program. The study was published in the peer-reviewed New England Journal of Medicine.

Most papers concentrated on the finding that it is the quality of food rather than calorie counting that can help people lose weight. The Express headline that doing this is the ‘easy way to lose weight’ and that the finding will help people ‘keen to shed excess pounds for the beach this summer’ was perhaps over-optimistic, as the paper looked at quite small weight changes over a period of many years. The Express included comments from independent experts. The Telegraph’s advice in its headline to consume ‘extra helpings’ of yoghurt and nuts could also be misleading.

 

What kind of research was this?

This research looked at the relationships between changes in lifestyle, diet and long-term weight changes. The study was based on three separate prospective cohort studies that included 120,877 men and women in the US.

The researchers point out that advice to ‘eat less and exercise more’ would seem to be straightforward but that weight gain often occurs gradually over decades – on average about half a kilogram (1lb) a year is gained, making it difficult for most people to distinguish the specific causes.

While many studies have evaluated different lifestyle behaviours separately and often at one point in time, their aim was to investigate the relationship between multiple lifestyle changes and long-term weight gain in studies that had followed people up over time (prospectively).

 

What did the research involve?

The researchers based their study on three large cohorts of American men and women whose health and lifestyles have been followed over many years, with the first cohort enrolled in 1976. All participants in these cohorts have been followed with two yearly, validated questionnaires focusing on their medical history, lifestyles, health practices and weight changes.

For the purposes of this study, researchers excluded anyone who was obese or who had a chronic disease, or for whom there was incomplete data. This left a total of 120,877 people. In two of the cohorts, participants were followed from a 1986 baseline to 2006 and in the third, they were followed from 1991 to 2003.

Researchers investigated the association between weight change and lifestyle habits (physical activity, TV watching, alcohol use, sleep duration, diet and cigarette smoking). On diet, they assessed people’s intake of fruits, vegetables, whole grains, refined grains, potatoes (boiled, mashed or fried), crisps (potato chips), whole fat dairy products, sugar-sweetened drinks, sweets and desserts, processed meats, unprocessed red meats, fried food and transfats. They also evaluated nuts, pure fruit juice, diet sodas, other types of dairy products and different types of alcoholic drinks.

Validated statistical methods were used to assess the independent association between changes in these lifestyle behaviours and changes in weight, within four-year periods. The findings were adjusted for other factors that might affect weight such as age and body mass index at the start of the study.  As the results for each cohort and for men and women were similar, the researchers pooled these results.

 

What were the basic results?

Researchers found that within each four-year period, participants gained an average of 1.5kg (3.35lb) (between five and 95% of the participants lost between 4.1 and 12.4).

Average weight gain for each four-year period was most strongly associated with eating crisps (800gm or 1.69lb gained), potatoes (600gm or 1.28lb gained), sugar-sweetened beverages (450gm or 1.00lb gained), unprocessed red meats (430gm 0.95lb gained ), and processed meats (400gm or 0.93lb gained).

Average weight gain over the same periods was inversely associated with the intake of vegetables (100gm or 0.22lb lost), whole grains (170gm or 0.37 lb lost), fruits (200gm or 0.49lb lost), nuts (259gm or 0.57lb lost), and yoghurt (370gm or 0.82lb lost).

Other lifestyle factors were also independently associated with weight change. These included physical activity (800gm or 1.76lb lost); alcohol use (200gm or 0.41lb gained for each daily drink), smoking (new quitters - 2.4kg or 5.17lb gained; former smokers - 60gm or 0.14lb gained), sleep (more weight gain with less than six hours or more than eight hours of sleep), and TV watching (140gm or 0.31lb gained for each hour a day).

 

How did the researchers interpret the results?

The researchers say they found many lifestyle factors were associated with long-term weight gain, including the consumption of specific foods and beverages. They point out that for many non-obese healthy people, long-term weight gain is gradual and accumulates over time, but that even modest increases in weight have implications for health. Although weight changes associated with any single lifestyle factors were modest, taken together, dietary factors and other lifestyle changes account for large differences in weight gain.

They point out that eating processed and refined foods and sugars can increase weight gain, but that when greater consumption of all different foods was taken into account, vegetables, fruits, nuts and whole grains were associated with less weight gain. They say that these foods obviously still provide calories and ‘cannot violate thermodynamic laws’, suggesting that consuming more of these foods reduces the intake of more calorific foods and that high fibre content and slower digestion keep people fuller for longer. Yoghurt was also associated with less weight gain, a finding they suggest may be due to changes in colonic bacteria.

 

Conclusion

There are several points of caution relevant to the newspaper reports:

  • The calorie content of foods was not measured in this study, but estimated from average portion sizes and the results of the dietary questionnaire. The researchers acknowledge this is not an accurate way of estimating total energy intake. Furthermore, they say that all these relationships between different foods and long-term weight gain must be influenced by changes in energy intake, energy expenditure or both. By this they mean that although food types are linked to weight gain or loss in their study, the underlying mechanism for weight loss will be a reduction in energy ‘in’ or an increase in energy ‘out’. Directly countering the claim that losing weight is simply a case of eating more nuts.
  • There were major changes in the population energy intake over the time of these studies. Between 1971 and 2004, the average dietary intake of calories in the US increased by 22% among women and by 10% among men who ate more refined carbohydrates, starches and sugar-sweetened beverages. This degree of change might not apply to the UK.
  • The study looked at long-term weight changes in people in the US who were not obese. Its findings are not necessarily applicable to people in the UK who are obese and who may need specialist nutritional help to lose weight.

This was a large, well-designed study, conducted over a lengthy period, so its findings on diet, lifestyle and weight gain are likely to be reliable. For most people, gradual weight gain, caused by a small but habitual energy imbalance, occurs over many years, so the researchers’ suggestion that modest changes in lifestyle could mitigate or reverse this is of value. It also supports current advice to eat a healthy diet, based on whole grains and a variety of fruit and vegetables.

As the authors make clear, simply adding specific components, such as nuts or yoghurt, to the diet without removing others will not achieve weight loss.

Analysis by Bazian

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Want to lose weight? Then eat extra helpings of yoghurt and nuts. The Daily Telegraph, June 23 2011

Dieters told: Quality of food, not quantity, is what counts. Daily Mail, June 23 2011

The easy way to lose weight. Daily Express, June 23 2011

Links to the science

Mozaffarian D, Hao T, Rimm EB, et alChanges in Diet and Lifestyle and Long-Term Weight Gain in Women and Men. New England Journal of Medicine 2011; 364: 2392-2404

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