Monday March 8 2010
The research does not suggest that wine is slimming
“Women who like a glass of wine after work are less likely to gain weight than those who stick to mineral water,” according to The Times, which claims that moderate female drinkers have a lower risk of obesity than teetotallers.
The research behind these claims asked a group of middle-aged American women of a healthy weight about their alcohol consumption. The women were sent follow-up questionnaires over the next 13 years to track how their weight changed. Over the course of the study most of the women gained weight, but on average those who originally consumed at least four units per day gained around 2kg less than their non-drinking counterparts.
While this study has found that higher alcohol consumption was associated with slightly lower weight gain over time, there are a number of limitations to the research. Equally, the study did not look at potential mechanisms by which alcohol could have an effect on weight, although it suggests that drinkers may have replaced dietary calories with calories from alcohol. However, the negative health effects of regular alcohol consumption are well-known, and women are advised to limit alcohol consumption to two to three units per day.
Where did the story come from?
This research was conducted by Dr Lu Wang and colleagues from Brigham and Women’s Hospital and Harvard University. The study was funded by the US National Institute of Health and published in the peer-reviewed medical journal Archives of Internal Medicine.
Several newspapers have reported on this research, with some suggesting that alcohol may aid weight loss. However, the research did not directly prove that alcohol consumption prevents weight gain, instead showing that the dietary and exercise habits of drinkers versus non-drinkers differed. Some news sources also reported on a theory that alcohol may be broken down in the liver to create heat rather than fat. That theory was not tested by this research.
What kind of research was this?
This was a prospective cohort study following a group of American women of normal weight to look at how their drinking habits affected the likelihood of them becoming overweight or obese over time.
The researchers say that alcohol contains 7.1 calories per gram and that the extra calories it contributes to the daily diet may increase weight gain. They add that studies have not provided consistent evidence that alcohol consumption is a risk factor for obesity. The researchers therefore used data from a large prospective cohort study in women to see whether there was any association between alcohol consumption and obesity in women.
What did the research involve?
The researchers drew participants and data from the Women’s Health Study, a randomised clinical trial that evaluated the effects of low-dose aspirin and vitamin E in the prevention of cancer and cardiovascular disease. The trial involved 39,876 female healthcare professionals aged 39 to 89 who were free of cancer and cardiovascular disease. For this subsequent alcohol study the researchers included 19,220 women with a body mass index (BMI) ranging from 18.5 up to 25, which is considered to be within the healthy range.
At the start of the study the participants were given a questionnaire asking how many alcoholic drinks they consumed. The frequency was graded in nine possible responses that ranged from “never or less than once per month” to “more than six times a day”. Their alcohol consumption was calculated according to the alcohol content in each type of beverage. The researchers defined one alcoholic unit as containing 8g of pure alcohol.
At the start of the study the researchers also collected baseline information on each participant’s age, smoking status, physical activity level, menopausal status, postmenopausal hormone use, multivitamin use, history of diabetes, hypertension (high blood pressure) and high cholesterol levels. The participants also completed a food frequency questionnaire that assigned a portion size for each specified food item. These were used to calculate an estimate of each participant’s calorie intake.
Information on the participants’ body weights was updated using follow-up questionnaires given 2, 3, 5, 6 and 9 years after the first questionnaire. In addition 16,322 of the women agreed to be followed up for a further four years, providing a dataset spanning 13 years from the initial questionnaire.
The women had their BMI calculated and categorised as normal (18.5-25), overweight (25-30) or obese (over 30). If a participant became overweight or obese while being followed up, the year in which this event occurred was recorded. If a woman developed diabetes, the date of the diagnosis was also recorded.
When the researchers performed their initial analysis they only adjusted their data to account for the women’s ages. As additional factors may have affected the women’s weight, the researchers made further adjustment to account for BMI at baseline, non-alcoholic energy intake and the type of food they ate (such as fruit and vegetables, meat, refined or whole grains, fibre and dairy produce). They also adjusted for the amount of exercise they did, their smoking status, hormone status, and any history of high cholesterol or high blood pressure.
What were the basic results?
The women’s baseline characteristics at the time of the first questionnaire showed that those who drank greater amounts of alcohol were more likely to be older, white, current smokers, postmenopausal, have high blood pressure and have a lower baseline BMI. They also found that although the total energy intake was greater in women who drank lots of alcoholic beverages, these women took in fewer calories from food than the non-drinkers.
Alcohol intake was associated with a greater intake of red meats, poultry and high-fat dairy products but a lower intake of whole grains, refined grains, low-fat dairy products, fats, carbohydrates and fibre. Women who consumed an intermediate amount of alcohol did more exercise than those who did not drink, or those who drank greater amounts. On average, all women put on weight over the follow-up period. However, the greatest average weight gain was in the women who did not drink alcohol.
The drinking and non-drinking groups had varied in a number of dietary and lifestyle factors at the start of the study, leading the researchers to perform a set of analyses that were adjusted to account for the influence of these variations. After these adjustments, they found that the relationship between weight gain and low alcohol consumption was stronger.
The researchers also found that 41.3% of the women had become overweight or obese during the follow-up period. When using a BMI of 30 as a cut-off, 3.8% of the women had become obese. The mean weight gain during 12.9 years of follow-up was 3.63kg for women who did not consume alcohol, compared to 1.55kg for those who consumed 30g per day or more. (95% confidence interval [CI], was 3.45-3.80kg vs 0.93-2.18KG).
How did the researchers interpret the results?
The researchers concluded that light-to-moderate alcohol consumption was associated with less weight gain and a lower risk of becoming overweight and/or obese over 12.9 years of follow-up in middle-aged women.
They suggested that other studies have shown that in British men, an equivalent increase in alcohol consumption was associated with increased BMI. They suggest that “male drinkers tend to add alcohol to their daily dietary intake, whereas female drinkers usually substitute alcohol for other foods without increasing total energy intake”.
This large cohort study that followed middle-aged women for almost 13 years found that there was an association between greater alcohol consumption and slightly slower weight gain over this period.
Despite the tone of press coverage, it should be remembered that this type of study can only show associations between factors, and cannot say how or whether alcohol directly causes the slower weight gain. There are also a number of limitations to this research, some of which the researchers have highlighted:
- The participants self-reported their weights and alcohol consumption, which may have resulted in a misclassification or underestimation of these values.
- The study used a single measurement of alcohol consumption taken at the start of the study. It is likely that the participants’ drinking habits changed over the 13-year study period.
- The questionnaire used in the study did not collect sufficient detail on some aspects of the women’s drinking habits. For example, it did not differentiate between women who drank a small amount on most days of the week and those who drank multiple drinks on one day of the week. These drinking patterns may have different effects on the body’s metabolism.
- The women in this study were predominantly white, female healthcare professionals who may differ in their socioeconomic status from other women, so these findings may not apply to the population as a whole or to men.
- The women included in this study were all originally in the healthy BMI range. This means the study has not looked at how the weight of women outside this range changes in relation to alcohol intake or whether alcohol may have contributed to existing weight problems.
- The average difference in weight gain between the groups was relatively small, at just over 2kg.
Given the limitations of this research, it is not possible to say whether alcohol consumption directly reduces the chances of weight gain. However, the data from this study contributes to our understanding of how related lifestyle factors such as alcohol consumption and eating habits can contribute to weight gain.
Excessive alcohol consumption is known to be bad for our health in several ways. For example, it can increase the risk of cancer and depression. Women are recommended to drink no more than two to three units a day. The daily limit for men is three to four units.