The Sort of Dairy Makes All the Difference

Summarized by Robert W. Griffith, MD
February 19, 2007

Summary

Women who consume more than one serving a day of whole milk, sour milk, or cheese are less likely to gain weight than those who consume lesser quantities of these dairy products.

Introduction

Everyone eats dairy foods of one sort or another. The trouble is we don't know which dairy products contribute most to weight changes. We recognize they are a major source of saturated fat, which is an obvious risk factor for cardiovascular disease. But they also carry benefits, such as suppliers of protein, calcium, and other nutrients. Randomized trials have produced little evidence of an effect of dairy products on body weight; however, such studies are usually of short duration.

An attempt has been made in Sweden to study the relationship between changes in dairy products consumption and body weight over a 9-year period in almost 20,000 women. The results, published in the American Journal of Clinical Nutrition, do not clarify the situation completely, but they do shed some light on which type of dairy products "carry the most weight". Here's a summary of the findings.

What was done

The participants selected for the study were perimenopausal (40 to 55 years at baseline), because of the vulnerability to weight gain induced by hormonal changes; in Sweden, the average weight gain among women is highest in this age group. The participants came from the Swedish Mammography Cohort, which was located in two counties in central Sweden. At baseline they completed a questionnaire covering height and weight, dietary intake, education, and parity. Between 7 and 10 years later an extended follow-up questionnaire was completed. After exclusion of those with incorrect or missing information, people who had suffered from a disease which might affect body weight, or changes in body mass index (BMI) greater than two points a year, there were 19,352 women with data available for analysis.

The initial questionnaires included a 67-item food frequency questionnaire. The following dairy groups had to be scored as consumed over the last 6 months "never-or-seldom" through 8 graded options up to "4-or-more servings per day":

Whole milk - 3% fat
Medium-fat milk - 1.5% fat
Low-fat milk - 0.5% fat or less
Whole sour milk - 3% fat
Low-fat sour milk - 0.5% fat
Cheese - 80% fat
Butter - 80% fat

The second questionnaire, 7-10 years later, was similar, but asked about consumption of the items during the previous 12 months. For the purposes of analysis, the products whole milk and whole sour milk were "collapsed" into one category, as were low-fat milk and low-fat sour milk.

Based on the answers to the questionnaires, for each of the five categories of dairy products, the participants were placed into four groups according to their change in intake of these dairy foods during the study:

Constant -- less than one serving a day
Increased intake -- an increase from less than one serving to one serving or more per day
Constant - one or more servings a day at both baseline and follow-up
Decreased intake -- a decrease from one or more servings to less than one serving a day

Body weights were reported to the nearest 0.1 kg. The average yearly weight change during the study was calculated, and the participants classified into two groups according to whether they gained less or more than 1 kg/year. The BMI at baseline was calculated, allowing analyses to be done in normal versus overweight women at baseline. And participants were classified into never, current and former smokers based on the second questionnaire. Physical activity was measured as time spent walking or bicycling, and the participants categorized into three groups.

What was found

The average age at baseline was 46, and the average BMI was 23.7. The average duration of the follow-up period was 8.8 years, and weight gain was 0.33 kg/year.

Just looking at the baseline data, the study showed that for whole milk and sour milk (the 3% category), cheese, and butter, the BMI scores were significantly higher in those with a high intake than a low intake. On the other hand, for low-fat milk and sour milk (0.5% fat) the BMI scores were significantly lower in those with a low intake.

Now consider the changes over the 9 year period. In those with a constant intake of whole milk and sour milk and cheese of 1 serving a day or more, which remained unchanged during the study, there was a significantly lower risk of gaining more than 1 kg weight a year than in those with a lower intake. There were no significant differences for women who increased or decreased their intake of 3% fat or cheese over the study period, but there were trends indicating similar effects; those who increased their intake had a lower risk of weight gain more than 1 kg/year, and those with a lower intake had a higher risk.

The separate analyses of overweight and normal-weight women showed that the findings remained significant for cheese and, for normal-weight women only, for whole milk and sour milk.

There were no clear trends for medium-fat milk, butter, or calcium intake (including calcium supplements).

What's the bottom line?

This is an important study, for several reasons. First, it's a 'real-life' study, rather than a rigid trial that can introduce artificiality into the results. Second, it was done in Sweden, a country with a relatively high dairy intake. Third, the subjects were perimenopausal women, who are at increased likelihood to develop weight change over these particular years.

In view of these qualities, it may seem disappointing that the results of the study were not more pronounced or clear-cut. They are not particularly easy to grasp, but they are consistent. The chief robust message is that regular consumption of one or more servings of dairy foods containing at least 3% fat are unlikely to increase body weight in normal-weight women; only cheese shows this effect in overweight women (BMI over 25).

This does not mean that all you have to do to lose weight is drink lots of milk and eat even more cheese. Increasing your intake of these products to more than one serving a day will be associated with an increase of calories and saturated fats - both of them undesirable results. It would be better to take the information for what it is - a small contribution to our knowledge on the complicated effects of dairy produce, which require further research to explain the practical benefits they can have.

Source

• Association between dairy food consumption and weight change over 9 y in 19,352 perimenopausal women. M. Rosell, NN. Hakansson, A. Wolk, Am J Clin Nutr, 2007, vol. 84, pp. 1481--1488

Related Links
Moderate-Fat Diets for Weight Loss?
Are Low-Fat Diets the Best Way to Lose Weight?
Milk Benefits More Than Just Bones

Please take a moment to give us your comments. For questions about Health matters you may check our "Questions & Answers" Portal and Service.