Because weight gain creeps up on us (or at least in this study population of non-obese individuals), the authors suggest it is more difficult to know what’s contributing to weight gain, which averaged 16.8 pounds over a 20-year study period. And so they undertook this colossal venture to find us the answers. Well, at least they tried to.
Before I share my reaction to the studies’ results, conclusions and media frenzy, let me state that I have no financial interest in the National Potato Growers Association (is there one, even?). Or, I might add, with Coca Cola and PepsiCo. But I do have a vested interest in not propagating diet myths. And it is this fear of public misinformation that drives me to invest the time reading the full research article (all 13 pages), which I suspect many of the popular press’ journalists failed to do.
My conclusions on the Harvard study
That is, unless you are underweight or anorexic; these populations tend to overestimate portions. And beverages are most notoriously challenging for us to estimate (unless of course they are in a marked can). When I have people measure their drinking glasses at home to determine just how much soda they drink, they are shocked. What they assume to be 8 ounces is typically double that amount.
Prepackaged food items and individual units will naturally be more accurately evaluated—individual yogurt cartons and fruits, for instance. Even grains that we tend to measure may be easier to assess, such as oatmeal, rice and cooked whole grains. These very foods that we are more likely to accurately assess our portions of, tend to be lower in calories. Without a doubt, this could distort the study's findings.
Sometimes a potato isn’t just a potato
How do you make mashed potatoes? I’ve heard of recipes that include a whole stick of butter, and some with only half a stick; there are those that add heavy cream and those that add a splash of milk. What’s my point? Did the researchers have information about the contents of these mashed, boiled, and baked potatoes, before concluding that it was the “refined carbohydrate” that was the culprit here leading to weight gain? The study emphasizes that it’s not about calories per serving. But here’s the problem: the serving size is not measured in the study, and we simply can’t make any conclusions about caloric density, if we don‘t even know the content, never mind the quantity, of what’s really in each portion!
Food selection may be a marker for more conscientious eaters
A colleague once said “if she’s eating rice cakes for breakfast than she’s not too serious about gaining weight”. Point well taken. Those who take the time to cook whole grains, such as brown rice, quinoa and buckwheat, are not likely to be the frequent diners at McDonald’s. Perhaps we could say the same for yogurt and low fat dairy eaters. Does anyone start drinking skim milk because of the taste? Eating these foods may simply identify those people who care about their health and the direction of their weight. Weight change may have nothing to do with the individual food itself.
Lifestyle changes they should have assessed
In their next study perhaps they should look at variables that truly impact our weight. Here are a few questions for their next questionnaire:
Secrets hidden in the Study that nobody advertised
For all of you Zone Diet and Atkins followers believing that more protein is good and carbs are bad, think again. This study showed that over time, meats, both processed and unprocessed types, were associated with weight gain. So if you are still stuck in the need for more protein for weight management, heed the warning. But remember, this is based on self-reported portions, a potential flaw in this study!
So it’s notable to me that yogurt and low fat dairy products as a category (adjusted by age) significantly link with decreasing weight over time. Why notable? Because Walter Willett, one of the study authors, has never been fond of supporting milk consumption. In previous presentations promoting his Mediterranean Oldways Diet Pyramid, he spoke strongly against inclusion of milk and milk products.
Never shy to ask my questions at conferences, I pressed him on this subject some time ago. His response fell short. He emphasized that some have intolerances to milk, and generalized about milk’s high fat content. And what about low and non-fat diary? And what about Lactaid milk for the intolerant? The majority of the population does not have a milk allergy, so why such an omission of dairy for the general healthy population? Let’s acknowledge that low fat dairy and yogurt are valuable, based on this study’s data.
There was no meaningful association between diet soda intake and weight change over time. Drinking it isn’t likely to cause weight loss. And contrary to previous media hype, diet soda won’t result in increasing weight either. But it certainly doesn’t add anything nutritionally to your intake. And, consuming it may displace some milk, which definitely does have its merits.
Exercise itself didn’t link with weight change, but a change in exercise level did. One more time?
If you’ve been doing the same amount and intensity level of physical activity over years, what happens? Well, think back to when you first started to exercise. It was quite a workout. But after doing it consistently for a while, it got easier. And with greater ease, you weren’t working as hard. And when you weren’t working as hard, you were burning fewer calories. And if you were using up fewer calories, over time, even if your eating remained the same, you would gradually gain weight. For the under eaters and over exercisers among you, let me remind you that you are not at any advantage if you continue to restrict you calories, relative to your need, while exercising. You, too, will suffer, ultimately breaking down the very muscle you aim to increase, and slowing your metabolic rate.
Still reading? Here's the take home message!
So what have the Harvard researchers really taught us? To be critical readers of the media, and of research, for starters. To recognize that studies like these are merely looking at associations, between weight change and changes in foods, and in lifestyle factors. We still don’t know why the link between potato products and weight gain. Maybe if we controlled for serving sizes and preparations we’d see a link with caloric density and weight gain. But maybe not.
I support inclusion of whole grains, fruits and vegetables and yogurt in our diets. But I also know that there’s a place for white, refined carbohydrate sources such as pasta, rice and low fiber French toast. And do I need to emphasize there’s a place for chocolate?
It may be, with more information, we will find some valuable links about foods and their impact on our fullness, affecting our weight over time. But I’d be a lot more cautious, and the media ought to be too, about labeling foods as bad versus good, perpetuating the myth information that causes us to stress eat.