Full-fat or low-fat? Recent US health advice has complicated the issue. Photo / Getty Images
Professor Walter Willett has studied nutrition for 50 years. He explains what the science says about dairy.
If you are confused about the role of milk and other dairy foods in a healthy diet, you are not alone.
For decades, national guidelines have recommended that Americans consume at least three servings a day of dairy foods, with the caveat that these should be low in fat because of the high amount of saturated fat and its link with heart disease.
However, a recent review concluded that consumption of milk, yogurt and cheese, irrespective of fat content, is “neutrally” associated with risk of cardiovascular disease, meaning that neither whole-fat nor low-fat dairy raises your chance of heart attack or stroke more when compared with other foods.
Is it really true that dietary advice has been wrong for decades and that recent research and data synthesis refute earlier guidelines on dairy foods and, more specifically, low-fat versions?
The reality is not simple and, more importantly, relates to what the researchers mean by “neutral” and what foods milk is being compared to.
Dairy fat has a high content of saturated fat; it makes up about two-thirds of total dairy fat. Also, dairy fat contains low amounts of the essential polyunsaturated fats.
Saturated fat gained attention in the 1960s because international comparisons showed a strong correlation between per capita intake of saturated fat and rates of heart disease, meaning countries with the highest intake of saturated fat also had high heart attack rates. Subsequently, dozens of randomised studies found that saturated fat increased blood levels of total and LDL (bad) cholesterol - both established risk factors for heart disease - when compared with the same number of calories from unsaturated fats.
Saturated fat similarly increased cholesterol levels when compared to carbohydrates, leading to the production of “low-fat” or “fat-free” packaged goods using refined grains or sugar as replacements. However, this ignored findings that this substitution also had adverse effects on other blood lipids that could negate the reductions in cholesterol levels.
Large studies of people followed for many years have found that consumption of dairy foods is minimally associated with risks of cardiovascular disease, leading to conclusions that dairy fat is “neutral”.
However, in these analyses, dairy foods are compared with a mix of other, mostly unhealthy sources of calories, such as refined grains, sugary beverages, other forms of sugar, red and processed meats, and, until recently, partially hydrogenated oils.
Thus, a lack of association with cardiovascular disease, or being “neutral”, simply means that dairy foods as a group are about as unhealthy as the mix of the other foods in the study population. Being “neutral” does not mean that consuming more of these foods has no health implications if compared with, for example, nuts or soy foods.
Studies of specific food comparisons are needed because we make those comparisons every day. For example, if we are making or ordering a sandwich, we might consider cheese, peanut butter or salami.
However, eating plant sources of protein such as nuts, soy and other legumes instead of dairy foods was associated with a lower risk of cardiovascular and total mortality, but eating red meat instead of dairy foods was associated with higher risk of these adverse outcomes. Notably, in this study, incremental amounts of full-fat milk were associated with increases in cardiovascular and total mortality, but low-fat milk consumption was not.
If you want to optimise your health, here are some research-based tips:
- Unsaturated plant sources of fat, such as soybean, canola or olive oil, will be better for long-term health than dairy fat.
- If you want to consume dairy foods, fermented products such as yogurt or cheese may be the best choices.
- As always, the amounts are important; one serving a day of full-fat dairy food will have only a small effect on your cardiovascular disease risk. In other words, if you have just one serving a day, the fat doesn’t make much difference.
- If you choose a low-fat dairy food, the calories replacing the fat are important; sugar and refined starch would not be an improvement and could be worse. Instead, emphasise healthy sources of fat or protein such as plant oils or nuts.
- Keep in mind that whole milk contains 3.25% or more of milk fat, low-fat milk has 1 to 2%, and skim has about 0.5%. All have the same nutrients, vitamins and minerals, regardless of whether some of the fat has been removed.
- For your protein needs, emphasise plant sources such as nuts, soy and other legumes instead of higher amounts of dairy foods. Want a second glass of milk? Consider minimally sweetened soy milk as an option.