Several readers sent me links today to various articles about a new study that blames potatoes for making us fat. Here are the headlines with some quotes:
Consuming an extra helping of potatoes each day — French fried, baked or otherwise — can add an average of 0.8 of a pound to body weight per year, researchers find. Over time, that can result in substantial weight gain.
Everyone knows that people who chow down on french fries, chug soda and go heavy on red meat tend to pile on more pounds than those who stick to salads, fruits and grains.
But is a serving of boiled potatoes really much worse than a helping of nuts? Is some white bread as bad as a candy bar? Could yogurt be a key to staying slim?
The answer to all those questions is yes, according to the provocative revelations produced by a big Harvard project that for the first time details how much weight individual foods make people put on or keep off.
The edict to eat less and exercise more is far from far-reaching, as a new analysis points to the increased consumption of potato chips, French fries, sugary sodas and red meat as a major cause of weight gain in people across the United States.
I have mixed feelings about the media coverage of this study. It’s encouraging to see something other than sugar or fat getting the blame for all our ills:
The problem, said study coauthor Dr. Walter Willett, chairman of the nutrition department at the Harvard School of Public Health, is that “we don’t eat potatoes raw, so it’s easier [for the body] to transform the starch to glucose.”
Since spuds prompt a quick increase in blood sugar levels, they cause the pancreas to go into overdrive trying to bring levels back down to normal. As blood sugar spirals down, people usually experience hunger, which leads to snacking. Over many years, this cycle can result in drastic weight gain and a fatigued pancreas, possibly contributing to the development of Type 2 diabetes.
It’s also encouraging to see the message getting out that weight loss isn’t as simple as counting calories:
The findings add to the growing body of evidence that getting heavier is not just a matter of “calories in, calories out,” and that the mantra: “Eat less and exercise more” is far too simplistic. Although calories remain crucial, some foods clearly cause people to put on more weight than others, perhaps because of their chemical makeup and how our bodies process them. This understanding may help explain the dizzying, often seemingly contradictory nutritional advice from one dietary study to the next.
“Our take-home message is what you eat affects how much you eat,” Mozaffarian said. “It’s not just a blanket message about reducing everything. Each individual lifestyle factor has a pretty small effect by itself, but the combined effect can explain that gradual weight gain.”
That’s why I don’t eat potatoes anymore, in spite of dire warnings from strange people who seem emotionally invested in convincing me I’m in mortal danger of permanently losing my tolerance for them: starches ramp up my appetite, period. They also spike my blood sugar. That may not happen to everyone, but it sure happens to me.
So I’m happy to see media articles warning people about consuming chips, fries, and other glucose-bombs. On the other hand, the study itself isn’t exactly what I’d call strong evidence. The researchers extracted their data from three large, multi-year observational studies. We all know what that means: food-recall questionnaires, which are notoriously inaccurate.
The message, at least as it’s being reported in the media, is also inconsistent. The news stories mention a plausible mechanism for how potatoes might encourage weight gain – potatoes spike glucose, which raises insulin, which drives fat storage – but then note that red meat was also associated with weight gain, while whole grains weren’t. If insulin-spiking potatoes are fattening, why isn’t insulin-spiking whole-grain bread?
Worst of all (though hardly surprising), the study is being reported as if the researchers have pinpointed cause and effect:
The researchers did find other culprits. For each additional sugary soft drink consumed per day, participants in the study gained an average of 1 pound over four years. Extra servings of red meats and processed meats did only slightly less damage.
Meats doing damage … yup, that sounds like cause and effect to me.
“I think it’s an important study,” said Kelly D. Brownell, director of Yale University’s Rudd Center for Food Policy and Obesity, who co-wrote an accompanying article. “It’s based on a large number of people followed over time, and it shows there are particular types of food that are contributing more than others to the obesity problem — and that some are protective against weight gain.”
No, Dr. Brownell, the study merely shows that some foods were associated with weight gain and some weren’t. We can’t conclude what’s actually protective and what isn’t from this kind of observational data. Fortunately, one expert quoted in the media made that very point:
“To attempt to isolate the effect of specific foods on weight changes is fraught with problems,” said Lawrence J. Cheskin, who heads the Johns Hopkins Weight Management Center. “One is that people may conclude that if they simply stop eating X, they will reduce the chance of weight gain. This is unlikely, and a false conclusion. Similarly, it is likely more a result of people who eat fruit being more health-conscious than fruit per se causing less weight gain.”
Bingo. Health-conscious people are different. They’re more likely to exercise, more likely to get enough sleep, less likely to eat potato chips, less likely to drink sodas, and – because they’ve been warned about it for 30-plus years – less likely to eat red meat, which is probably why red meat was associated with weight gain.
Yes, I believe potatoes and sodas make insulin-resistant people fatter. But I wouldn’t hold up this study as proof.