How drastically have new advances in science changed what we know about nutrition? This week, just a little. We're looking at three studies on potatoes, coconut oil and vegetarian diets.
Coconut Oil Loses Its Shine
The headline: Coconut Oil Is as Bad for You as Beef Fat and Butter
The story: Coconut oil is high in saturated fat, just like lard and butter, but it has a better reputation. It just seems healthier, you know? It makes your baked goods fluffy and your hair shiny. It may even have a small fat-burning effect (maybe, I repeat, maybe), but it's also a big pile of kilojoules just like any other fat or oil. So if you were thinking of it as a totally free, wholesome health food, you were already a little too optimistic.
Today's news is an advisory from the American Heart Association that says we should quit eating so much saturated fat. That includes coconut oil. But their studies don't specifically link coconut oil with heart disease, except to say that coconut oil raises LDL (bad) cholesterol as much as butter.
Cholesterol levels aren't the same as disease risk, and we can't ignore previous studies that say saturated fat may not be so bad for you. Dietary fat is actually a really tricky subject, and we still don't have clear answers on whether butter or coconut oil is harmful. It's fine if you want to back away from the coconut oil. But we don't have the evidence to say if that will make a real difference to your health.
The take-away: Coconut oil is full of kilojoules and saturated fat, so please don't think it's totally cool to eat in large quantities. If you use a lot of it in your diet (or butter or lard, for that matter), you might want to err on the side of caution and replace some of that with olive oil.
Fries Aren't Poison
The story: This actually comes from a study of people at risk of getting arthritis in their knees. To be included, they had to be overweight or have another reason to be especially likely to develop arthritis. When they signed up for the study, they answered a questionnaire about how often they ate different food groups in the past year.
The researchers don't say in their study whether they started off looking for data on the risks of potatoes, or whether they ran the analysis for every food in this study (and maybe other studies too?) and decided to report the one thing that turned up positive. If that's the case, the results become a lot less valid: If you look long enough, you'll almost always find something that seems significant. Either way, this study can't say whether eating fries is bad for you; it just says that people who ate a lot of fries had a higher mortality rate than people who didn't. This PopSci article explains the problems in a bit more detail.
There are two really important caveats here. The researchers didn't control for two very important factors: Whether people who ate fries happened to have a less healthy diet or lifestyle in total; and whether people who ate fries were lower income, which is definitely associated with worse health. And those are two big, big things to miss.
The take-away: This study does not support the idea that fries are deadly. But if you eat healthy, you probably won't have a ton of fries in your diet anyway.
Vegetarian Diets Are OK
The story: A vegetarian diet outperformed an omnivorous diet in one recent weight loss study... sort of.
The study involved 74 people who were all overweight and had type 2 diabetes. Half of them ate a diet that was vegan except for a serving of yogurt. The other half got a pretty standard diabetes management diet. The people on the near-vegan diet lost more weight, and were more likely to stick to the diet.
There's already reason to be sceptical: The study is small, and it was specific enough that if you're not diabetic, or if your idea of a vegetarian diet involves eggs and cheese, these results probably don't apply to you. Here's a more in-depth explanation of the study's limitations.
Another big caveat: The people on the vegetarian diet were also more likely to lose muscle, even though they were exercising.
The take-away: A very specific vegetarian diet worked well for some people, but the study is too small and limited to be generalised to all vegetarian diets for all human beings. There are a lot of different diets that work, but to find the right one for you, you'll just have to try and see.