What should a healthful diet include? If you had to make a list, you’d probably start with vegetables and fruits. After all, they feature prominently in both the DASH (Dietary Approaches to Stop Hypertension) diet and the Mediterranean Diet. We have plenty of evidence that both of those benefit blood pressure and help reduce the risk of diabetes. No doubt you’d mention whole grains like oats or brown rice. If you are not a vegetarian, you might list fish and possibly chicken. Perhaps you’d include low-fat dairy products (part of the DASH diet). But ice cream? We suspect you might have a bias against ice cream. Many nutrition scientists seem to share it.
A fascinating article by David Merritt Johns in the May 2023 issue of The Atlantic highlights this curious proposition. He starts with a doctoral dissertation defended at the T.H. Chan School of Public Health in Harvard University in 2018. The candidate, Andres Ardisson Korat, had done an extensive analysis of the relationship between dairy food consumption and cardiometabolic health–basically type 2 diabetes and heart disease. The data came from the Nurses’ Health Study, the Nurses’ Health Study II and the Health Professionals Follow-up Study. All of these carefully conducted long-term cohort studies have collected detailed dietary data from thousands of presumably reliable reporters (health professionals!) over the decades. As far as epidemiology goes, these studies are the cream of the cream.
Or maybe the cream of the ice cream. Because what (now) Dr. Ardisson Korat discovered was unexpected: “Intake of total dairy product or individual dairy products were not associated with CVD risk, with the exception of an inverse association between ice-cream intake and CVD health outcomes.“ To translate, people who ate more ice cream were less likely to have problems like heart attacks, strokes or coronary blockages requiring stents.
Is There a Bias Against Ice Cream?
According to Mr. Johns, this result prompted the candidate’s committee to push for further analysis. How could ice cream be linked to a lower heart risk? Nonetheless, despite further careful analysis, the association just wouldn’t go away.
Now, every statistician will tell you that association is not causation. We get that. However, as Mr. Johns describes, this is not the first time that analysis of the Harvard dietary data fingered ice cream as healthy. Twenty years ago, Mark Pereira found that people who reported eating ice cream were less likely to develop type 2 diabetes. When he spoke with Mr. Johns recently, Dr. Pereira admitted he still can’t explain it, but he insisted, “We analyzed the hell out of the data.”
Moreover, his study and the study by Dr. Ardisson Korat are not the only ones. Other analyses of dietary data, especially large data sets over long periods of time, have also found an ice cream signal. Why haven’t you heard about it?
What you have heard instead is that low-fat yogurt is good for you. The analysis showed that people eating yogurt were also less prone to type 2 diabetes. However, the ice cream signal was even stronger. So, why didn’t it make headlines?
Alternate Explanations:
One reason might be that the nutrition scientists just didn’t believe it. Consequently, they looked for another way to explain this anomaly. Here it is. They hypothesized that people who had developed health problems like diabetes or heart disease would probably have cleaned up their (dietary) acts and would be no longer eating indulgent desserts like ice cream. Scientists call this “reverse causation.” Of course, it is plausible, although the lack of such a signal for doughnuts or cake undermines it more than a bit. A more plausible explanation is a bias against ice cream.
Dr. Pereira offered Mr. Johns a somewhat different explanation. He pointed out that many of us shade the truth when we are answering questionnaires. In his study, heavier people reported eating fewer dairy-based desserts than people of normal weight. Perhaps they were trying hard not to gain more weight, but he suggested an alternate explanation: “I don’t believe that the heavier people consume less desserts,” he said. “I believe they underreport more.” That in itself might be evidence of a bias against ice cream, as well as a bias against overweight.
Nutrition Scientists Have Shown Some Biases Before:
If there were a bias against ice cream among nutrition scientists, it wouldn’t be the first one. We have been writing for years about dietary recommendations based more on dogma than on evidence.
To start with, experts warned us against consuming foods high in cholesterol. Butter and eggs were off the menu. Dairy fat in particular has a bad reputation. However, a new study suggests that people with prediabetes benefit from eating full-fat yogurt (American Physiology Summit, April 20, 2023). The participants consumed either fat-free yogurt for three weeks or full-fat yogurt for three weeks. Then they “crossed over” to eat the other yogurt for the final three weeks of the study. When these volunteers ate full fat yogurt, their fasting blood sugar dropped into the normal range, on average. Now, plain full-fat yogurt has far less sugar than ice cream, so the studies are not exactly comparable. But it does suggest that reactions to dairy fat need more research and that a bias against ice cream might not be completely justified.
Past Contradictions Complicate the Bias Against Ice Cream:
It wasn’t enough that people were staying away from cholesterol-containing foods. Next, they were told that all fat was bad. They were encouraged to dramatically cut fat intake. Many people turned to fat-free foods and fake fats to accomplish this goal, even though they didn’t taste as good.
Although consumers were warned away from whole milk (not to mention ice cream), they were urged to get lots of calcium to build strong bones. As a result, millions of women started swallowing calcium supplements to avoid osteoporosis. However, subsequent studies did not provide strong support for this (Climacteric, Oct. 16, 2015).
All these recommendations were presented as if they were chiseled in stone. The health gurus set them forth as facts rather than articles of faith. Little wonder, then, that we might suspect that at least some scientists have a bias against ice cream.
