Will Skim Milk Save You from Aging?

Skim milk can be whatever you want. To some people (we confess) it seems like a disgusting example of fake food. To others it’s an exemplar for healthy nutrition. For that latter crowd, a new study points to an association of slower aging with drinking skim or low-fat milk. Is this a benefit you can count on?

Health reporters are certainly spinning out headlines to make the casual reader think so. The press office at Brigham Young University tells us that drinking lower fat milk “accounts for 4.5 years of less aging in adults.” With apologies, we have to say that sounds like misleading spin to us.

Correlation with a Surrogate Marker

First of all, this is a study of correlation, not cause and effect. The researchers say it quite clearly in their paper:

Cross-sectional data cannot be used to infer cause-and-effect. Causation is a possibility, and the present findings warrant additional research in this area, but the scope of this study does not allow causal conclusions.

But that’s not what their press release says. It says that drinking lower fat milk “accounts” for less aging in adults. Merriam-Webster tells us that an accounting is a statement or exposition of reasons, causes, or motives. Thus, we see BYU’s press release as a clear example of misleading spin. It suggests that low-fat milk causes less aging than whole milk.

Even beyond the correlation, we have the issue of a surrogate marker. These researchers did not study actual signs and symptoms of aging. Instead they studied a convenient surrogate marker – telomere length. Certainly, it’s a measure that can be quite useful for researchers. But it has some serious limitations, too. Geneticist Ricki Lewis calls it “molecular palm reading.” She cites its limitations for predicting future health or longevity.

In short, at best, this study documents a correlation with an imperfect surrogate market for aging. That’s all.

Other Evidence

This study is hardly the whole story on whole versus low-fat milk. Kristin Hirahatake and an impressive group of nutrition researchers have a new paper summarizing the evidence base.  Published by Advances in Nutrition, their paper summarizes the potential cardiometabolic benefits of full-fat dairy products. They tell us that this science is still emerging and also lay out the need for further research. But we note that they say:

Although low-fat dairy is a practical, practice-based recommendation, its superiority compared with full-fat dairy is not obviously supported by results from recent prospective cohort studies or intervention trials.

Bottom Line

The fact is that Dietary Guidelines for Americans still recommend low-fat over whole-fat dairy. This continues even though the evidence for it is far from clear. Yes, dairy fat is mostly saturated fat. However, it’s not obviously clear that dairy fat has net negative cardiometabolic effects. In fact, there’s evidence to support the idea that skim milk is worse for your metabolic and heart health.

We need to be curious about the scientific truth relevant to this question. We shouldn’t be cherry-picking data to support our biases. Objectivity suffers.

Click here for the paper on skim milk and aging, here for the press release, and here for the paper on full-fat dairy.

Bottled, illustration by Caroline / flickr

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January 20, 2020