Meat consumption and weight gain

Author: Eoin O'Connell

Can reducing your meat consumption

help you lose weight? Image by

Beau96080 via Wikimedia Commons.

Last year, the American Journal of Clinical Nutrition published the results of a study of over 370,000 Europeans. A wide range of variables such as detailed dietary information, weight, height, gender, physical activity and smoking status were gathered from participants from several countries. The aim was to test if meat consumption was associated with five-year weight gain and in general the researchers found that it was. Specifically, when controlling for overall calorie intake, each 250g/8.8oz of meat consumed every day corresponded to a five-year increase in weight gain of 1.5 – 2.7kg (3.3 – 6 lbs). The tempting conclusion (as reported in at least one Australian daily newspaper and two very prominent news sources) is that reducing meat consumption by 250g per day could reduce weight by 1.5 – 2.7kg over five years. Considering that average weight gain over five years is around 2.3kg, this is a substantial decrease. What might not be immediately obvious is that a reduction of 250 grams per day would render about 68% of European women and 39% of European men vegetarian (i.e. they currently eat 250g or less of meat per day).

Before you forlornly grab the softer parts of your torso and google vegetarian recipes, there are some caveats to be gleaned from the original journal article. The breadth of the conclusions reported in the daily press make the information easy to digest but they fail to capture any exceptions in the association between meat consumption and weight gain. For example, meat consumption (of all kinds) was not associated with weight gain for those who were obese (Body Mass Index (BMI) >30) and those who were physically inactive showed no consistent weight gains due to red meat. Table 1 below is a summary of the effects of four important factors – age, BMI [weight in kilograms divided by height in meters squared (kg/m^2)], smoking status and physical activity – in the relationship between meat consumption and weight gain. Where N/A appears, the authors did not report the figures.

In light of the information in table 1, an alternative interpretation of these results could be: people who do some exercise and are not obese can gain weight (in the form of muscle mass) by eating more meat, particularly poultry if over 45 and red meat if under 45. Perhaps not so surprisingly, the consideration that muscle is a form of weight gain does not appear in the newspaper articles but much more surprising is the fact that it does not appear in the original journal article either.

In even the very best studies, there are inevitable weaknesses in the methodology and/or theory. Here are some of the authors' own thoughts on the limitations of this study:

"We measured diet only at baseline and were not able to consider change in diet before or during follow-up. However, we conducted sensitivity analyses...and the association persisted." The risk is that diet may have changed over the course of five years, however the authors seem satisfied that any variations could not have significantly changed their conclusions.

"[W]eight at follow-up was self-reported in most centers (sic) and was thus most likely underestimated. However, strong correlations have been observed between self-reported and measured weights." The strong correlations to which the authors refer are 0.97 for both males and females (out of 1), which are very high. These results come from a study on a sample of 263 US health professionals between the ages of 40 and 75 years. The issue of whether this sample is comparable to the European sample is a sticky one and can come down to individual perception. However, the authors do exercise considerable care in this case, employing two other methods to check the self-reported weight scores.

Overall, this is a good study with some important conclusions but bear in mind that these figures are averages over a very great number of people from several nations. Individual differences, genetic predispositions and lifestyle choices also play a part. By eating 250g less of meat every day, Hans in Germany might reduce his five-year weight gain by 2.5kg (5.5lbs) but Bella in Italy might reduce hers by just 1kg (2.2lbs).