Low Fat Dairy and Its Discontents

I’m not exactly sure what inspired Allison Aubrey to report on two research papers from last year as breaking news, but I’m glad she did, and glad her story has gained some legs.

New research suggests we may want to look anew.

Consider the findings of two recent studies that conclude the consumption of whole-fat dairy is linked to reduced body fat.

In one paper, published by Swedish researchers in the Scandinavian Journal of Primary Health Care, middle-aged men who consumed high-fat milk, butter and cream were significantly less likely to become obese over a period of 12 years compared with men who never or rarely ate high-fat dairy.

Yep, that’s right. The butter and whole-milk eaters did better at keeping the pounds off.

“I would say it’s counterintuitive,” says Greg Miller, executive vice president of the National Dairy Council.

The second study, published in the European Journal of Nutrition, is a meta-analysis of 16 observational studies. There has been a hypothesis that high-fat dairy foods contribute to obesity and heart disease risk, but the reviewers concluded that the evidence does not support this hypothesis. In fact, the reviewers found that in most of the studies, high-fat dairy was associated with a lower risk of obesity.

The reason I’m glad, is that this goes to a long running pet peeve of mine. All too often, the conventional wisdom in nutrition is unsupported by the data. Sometimes, it’s in direct contradiction.

When I first started becoming interested in nutrition, I came across a study headed by a Harvard study from 2005 that followed a group of 12,829 US children, aged 9 to 14 years from 1996 through 1999. The purpose of the study was to “assess the associations between milk, calcium from foods and beverages, dairy fat, and weight change over time.” Data was collected by surveys returned by mail. After looking at the data, these were their conclusions:

Children who drank the most milk gained more weight, but the added calories appeared responsible. Contrary to our hypotheses, dietary calcium and skim and 1% milk were associated with weight gain, but dairy fat was not. Drinking large amounts of milk may provide excess energy to some children.

At the time, it seemed interesting and counterintuitive and was duly filed away to some empty dendrites I had lying around. Not long after, in 2006, came news that New York City was removing whole milk from the public school cafeterias in order to combat childhood obesity. Low fat chocolate milk would be allowed, but whole milk would be banished. The report also mentioned that Los Angeles had done the same in 2000. It was reported that some states had made the same change or were considering it.

I had to wonder; had the nutritionist for a school system with 1.1 million students have missed the Harvard study? Was there other research that contradicted the 2005 study? Had anyone bothered to collect any data in Los Angeles to measure the impact of the change made in 2000? In 2006, those answers to those questions weren’t as easy to find for an amateur with a short attention span like myself. I was reduced to stewing on the fact that a very large public health intervention had been made in contradiction of the only research I could find on the issue. A huge pet peeve of mine is the willingness, especially in nutrition to undertake public policy interventions in the absence of any evidence that they will achieve the desired outcome. (I’m looking at you restaurant calorie postings.)

The one other thing I found on the issue at the time, was that hog farmers have been using skim to fatten hogs since your grandfather was in short pants. The observation that skim milk was particularly fattening was borne out by the research at the time. From the Station Bulletin, Oregon State Agricultural College – November 1930 [pdf]:

Skim milk. This is not only the very best supplement for growing pigs, but is of almost equal value for fattening purposes. Though very low in dry-matter content, milk furnishes a complete protein, which fact accounts in a large measure for the excellent returns. Milk renders the ration more palatable, inducing greater consumption and consequently greater daily gains. Also milk is a good source of minerals.

Granted, they weren’t comparing it to whole milk, but still … not a promising observation for Hansel and Gretel.

Sometime in 2011, I did finally follow up and gather all the relevant research I could find. The nearly dozen and a half papers I gathered at the time were nearly an exact match to those that the Kratz paper looked at.

METHODS: We have conducted a systematic literature review of observational studies on the relationship between dairy fat and high-fat dairy foods, obesity, and cardiometabolic disease. We have integrated these findings with data from controlled studies showing effects of several minor dairy fatty acids on adiposity and cardiometabolic risk factors, and data on how bovine feeding practices influence the composition of dairy fat.

RESULTS: In 11 of 16 studies, high-fat dairy intake was inversely associated with measures of adiposity. Studies examining the relationship between high-fat dairy consumption and metabolic health reported either an inverse or no association. Studies investigating the connection between high-fat dairy intake and diabetes or cardiovascular disease incidence were inconsistent. We discuss factors that may have contributed to the variability between studies, including differences in the potential for residual confounding; the types of high-fat dairy foods consumed; and bovine feeding practices (pasture- vs. grain-based) known to influence the composition of dairy fat.

CONCLUSIONS: The observational evidence does not support the hypothesis that dairy fat or high-fat dairy foods contribute to obesity or cardiometabolic risk, and suggests that high-fat dairy consumption within typical dietary patterns is inversely associated with obesity risk. Although not conclusive, these findings may provide a rationale for future research into the bioactive properties of dairy fat and the impact of bovine feeding practices on the health effects of dairy fat.

The literature gathered was from 1999 to 2011. As to my earlier question about what research had been available at the time the New York school district was making the decision to eliminate whole milk from their cafeterias, seven of the studies considered were available at the time. None of them supported the idea that removing whole milk from students diets would be helpful in combatting obesity. The clear majority suggested the opposite.

I had drawn the same conclusions looking at the same literature as Kratz and company did. But, I also wondered about the studies that did show a correlation between dairy fat consumption, adiposity and metabolic health. The paper’s authors noticed the same geographic pattern that I had.

Examining Table 1, it is clear that location has a major influence on the studies’ outcomes. Of the nine studies that were conducted in Europe, eight found that dairy fat intake
is inversely associated with adiposity. Of the seven that were conducted in the United States, three found an inverse association, while four did not. Three factors stand out as possible explanations for this discrepancy.

The first is the high potential for residual and unmeasured confounding in US cohorts. Since the 1980s, there has been a public health campaign in the United States to lower the consumption of SFA-rich foods such as animal fats. As a result, dairy fat is perceived as unhealthy in the United States, and one would expect its consumption to be associated with other behaviors that are perceived as unhealthy. Indeed, Liu et al. reported that US women in the highest quintile of high-fat dairy intake were 62 % more likely to be current smokers than women in the lowest quintile, whereas women in the highest quintile of low-fat dairy intake were 62 % less likely to smoke than the lowest quintile.

Similarly, dietary fiber intake was 21 % lower in the highest quintile of high-fat dairy intake compared to the lowest. Comparable trends were reported by Margolis et al., including substantially higher physical activity and income level in the top quintile of low-fat dairy intake, and substantially lower physical activity and income level in the top quintile of high-fat dairy intake [35]. This demonstrates the cultural stigma attached to dairy fat consumption in the United States, and casts doubt upon the ability of observational studies to fully adjust for the unhealthy lifestyle patterns that associate with dairy fat consumption in this environment.

Or as I would put it: Pizza and Cheeseburgers.
So it was unsurprising, when I learned later that week that, “that an astonishing 13% of the U.S. population consumed pizza on any given day”. More disturbing:

For this large population — more than 1 out of 8 Americans — who consumed pizza in a particular day:

• Pizza accounted for 25% (among kids) and 29% (among adults) of daily food energy intake. More than a quarter of all calorie intake was pizza.
• Pizza accounted for 33% (among kids) and 39% (among adults) of daily saturated fat intake. Compared with foods in general, pizza is much heavier in saturated fat.
• Pizza accounted for 33% (among kids) and 38% (among adults) of sodium intake. Compared with foods in general, pizza is much heavier in sodium.

In recent years, USDA’s dairy checkoff program has spent many millions of dollars to increase pizza consumption among U.S. children and adults. Using the federal government’s taxation powers, the checkoff program collects a mandatory assessment of 15 cents on every hundredweight of milk that is sold for use as fluid milk or dairy products. The total mandatory assessment in 2011 was $104 million for fluid milk and $98 million for other dairy products, according to the most recent annual USDA Report to Congress. These expenditures are many times greater than federal spending on promoting fruits and vegetables, whole grains, or any of the other foods for which the Dietary Guidelines recommend increased consumption.

I love it when a plan comes together. But, not always.

Sources:
The Full-Fat Paradox: Whole Milk May Keep Us Lean
Allison Aubrey | The Salt/NPR | 12 February 2014

High dairy fat intake related to less central obesity: a male cohort study with 12 years’ follow-up.
Holmberg S, Thelin A. | Scandinavian Journal of Primary Heathcare | June 2013

The relationship between high-fat dairy consumption and obesity, cardiovascular, and metabolic disease.
M Kratz, T Baars, S Guyenet | The European Journal of Nutrition | February 2013 | [pdf]

Milk, dairy fat, dietary calcium, and weight gain: a longitudinal study of adolescents.
Berkey CS, Rockett HR, Willett WC, Colditz GA. | Archives of Pediatrics and Adolescent Medicine | June 2005

In New York Schools, Whole Milk Is Cast From the Menu
David Herszenhorn | The New York Times | 2 February 2006

Fattening Pigs for Market [pdf]
Agricultural Experiment Station | Oregon State Agricultural College | Station Bulletin | November 1930

USDA reports on pizza consumption and on dairy checkoff program initiatives to increase pizza demand
Parke Wilde | US Food Policy | 7 February 2014