“Eat less meat to lose weight,” the Daily Express has reported. The front-page news says that people who love steak gain extra weight compared with non-meat eaters, even if they consume the same number of calories.
The news is based on a Europe-wide study of more than 370,000 people, which discovered that over five years heavy meat eaters gained approximately two kilograms more than those who rarely ate meat. Extra weight gain was particularly prevalent in those who ate processed meats such as bacon, ham and sausages. These results run contrary to the hotly debated theory that a diet high in protein prevents obesity or may promote weight loss.
In a study of this kind it is possible that unhealthy habits such as smoking, drinking too much and not enough exercise may be behind some of the results seen. However, these factors were taken into account in this well-conducted study. Because of this, and because of the study’s size and duration, we can have increased confidence in its results.
Where did the story come from?
The study was carried out by researchers from Imperial College, London and a number of other universities in Europe who were all part of the continuing EPIC-PANACEA research project. This group of studies are all funded by a variety of government, charitable and not-for-profit sources. The study was published in the peer-reviewed American Journal of Clinical Nutrition.
The debate about whether the meat content of a diet makes it easier or harder to lose weight centres around two competing ideas. On the one hand, because of its high energy density and fat content, meat consumption is thought to lead to weight gain. On the other hand, it has been suggested that a diet high in protein may lead to weight loss because it may make people feel full or increase their metabolic rate in some way.
Despite a headline that accurately presents the results of this study, the Daily Mail also suggests that calories in meat could be more fattening than those in other foods, which is itself controversial.
What kind of research was this?
The researchers say that several existing observational studies already show that increased meat consumption leads to weight gain. However, there is continuing uncertainty about whether the link is fully attributable to meat intake itself, and so there is a need to explore the issue with further research.
This was a large cohort study that followed a total of 103,455 men and 270,348 women recruited across 10 European countries over a period of five years. The researchers wanted to assess the associations between weight gain and the consumption of red meat, poultry, processed meat and total meat consumption. They had data available which had been collected between 1992 and 2000 in a study called the European Prospective Investigation into Cancer and Nutrition–Physical Activity, Nutrition, Alcohol, Cessation of Smoking, Eating Out of Home and Obesity project, or EPIC-PANACEA.
The study is large and reliable, with appropriate adjustments and controls to account for the influence of age, sex, total energy intake, physical activity, dietary patterns and other potential confounders that might also be associated with weight gain. The size of the study allowed the researchers to look specifically at the types of meat eaten, and the research may be the most reliable yet to examine these links.
What did the research involve?
The researchers recruited more than 500,000 initial volunteers (between 25 and 70 years of age) from 23 centres in 10 European countries: Denmark, France, Germany, Greece, Italy, Netherlands, Norway, Spain, Sweden and the United Kingdom. Only women were recruited at the centres in France, Norway, Utrecht (Netherlands) and Naples (Italy). They also excluded individuals who had incomplete data records, implausible weight changes or were pregnant. This left a population who were mostly women.
The researchers assessed diet at the start of the study using country-specific questionnaires in different languages. They tested these questionnaires for accuracy by directly observing the actual diets of a sample of participants. Weight and height were also measured at the time of the questionnaire. At follow-up sessions, weight and height were self-reported in most countries.
The methods of data analysis used (multivariate analysis) were appropriate, as they took into account factors other than meat consumption that could influence weight gain. The researchers looked primarily at the associations between energy from meat (kcal per day) and annual weight change (grams per year). They took into account age, sex, total energy intake, physical activity, dietary patterns and other potential confounders in their weight gain model.
What were the basic results?
Greater levels of meat consumption were associated with greater weight gain in men and women, in normal-weight and overweight subjects, and in smokers and non-smokers.
With adjustment for estimated energy intake, an increase in meat intake of 250g per day (about one steak) would lead to an additional 2kg of weight gain after five years (95% confidence interval 1.5-2.7kg).
The link was also statistically significant for red meat, poultry and processed meat.
There were interesting differences between countries, with highest averages of daily meat intake in the cohorts from Denmark, Germany, Spain, Sweden and the Netherlands (over 316 kcal from meat per day in men, 207 kcal in women). The lowest daily meat intakes were in Greece (193 kcal in men, 142 kcal in women) and in the Oxford ‘health-conscious’ cohort, which included mostly vegetarian subjects (86 and 82 kcal per day).
How did the researchers interpret the results?
The researchers simply say that their results suggest that a “decrease in meat consumption may improve weight management”.
They say that the results therefore support the public health recommendation to decrease meat consumption for health improvement.
This very large study was well conducted and may provide the best data so far looking at how meat eating relates to weight gain. The authors do comment that:
- As weight was self-reported after the first assessment it is likely that this was underestimated. They improved this by making adjustments to their analyses, and say that it is unlikely that their findings could be explained by inaccuracies in weight change.
- They were unable to consider change in diet before or during follow-up, as recruits only completed the dietary questionnaire once, at the start of the study. This too could have led to inaccuracies, particularly in people who regularly change diets or ‘diet cycle’ (repeatedly losing and regaining weight), which is itself a risk factor for obesity in men.
- Some research centres only selected women, which may have skewed the results.
Overall, the large size of this study and the high response rate (80.6%) over five years suggest that the research provides reliable results, which are probably also relevant to the UK.