The Bad Food Researchers Respond

Just a couple months ago, I posted this blog regarding a research study that was conducted by several scientists from Harvard and included Walter Willett.  In that study, certain foods were related to obesity.  Included in that list were potatoes.  Since the study was published in the NEJM some controversy has developed.  How could someone put a boiled and baked potato in the same category as a chip or fry and even snack cakes?!

This debate played out a little in a recent edition of the journal and the study authors responded to some of the posted letters.  I love their response and wanted to share it with you here.

Ideally you should go to this link and read the letters and the response in the proper context.  In case you cannot access it, I am replicating the author's response here.  I hope I am not breaking any laws in doing so.

The citation for the letters is:

N Engl J Med 2011; 365:1058-1059 September 15, 2011.

(the numbers you see in the text refer to the references the author's are citing)

All foods have calories, so differential effects on weight gain must relate to varying portions, accompanying calories, displacement of other foods, effects on hunger, satiety, and metabolism, or all of these factors.
In our analysis of potato subtypes, the greatest weight gain was associated with french fries, then potato chips, then boiled, baked, or mashed preparations. French fries and potato chips are often consumed in larger portions than other preparations of potatoes, and previously they often contained industrial trans fats. The use of trans fats, which has been greatly reduced in the United States, may have independent effects on the risk of obesity.
In our study, all potato preparations were linked to weight gain. The large amount of rapidly digestible starch is a likely culprit, producing many metabolic harms that are similar to those of refined sugars, including bursts of glucose and insulin, strained beta-cell function, and potentially increased later hunger,1 despite some nutrient value in potatoes. Their high glycemic load contributes to weight gain and an increased risk of diabetes and coronary disease.1-4 A focus on foods, rather than single constituents, facilitates translation to dietary recommendations and minimizes industry manipulation.5 Weight gain associated with boiled, baked, or mashed potatoes was similar to that associated with refined grains or sweets and desserts: calorie for calorie, there may be little difference among potatoes, corn flakes, white bread, or table sugar with respect to weight gain.
Blaming only toppings or “added fat” is unsupported. Butter was associated with less weight gain than potatoes, and cheese had no association. Consistent with randomized weight-loss trials, our findings provide no support for focusing on dietary fat alone. Weight gain was positively associated with fat-free foods, including refined grains and soda, unassociated with whole-fat milk and cheese, and inversely associated with nuts. Ironically, baked or low-fat french fries and potato chips have reduced amounts of their healthiest component — unsaturated vegetable oils — leaving mostly starch and salt.
Focusing on potatoes alone misses larger points about poor overall carbohydrate quality and diet patterns which are risk factors for obesity, diabetes, and coronary disease.4 Potatoes, soda, white bread, low-fiber cereals, sweets, and other processed and refined grain products should each be limited, and minimally processed foods such as nuts, fruits, vegetables, and whole grains should be increased. Global epidemics of obesity and chronic disease amplify both the health and economic imperatives of altering current agricultural and food-industry priorities. Many small dietary and lifestyle changes together make a big difference — for bad or good.

Dariush Mozaffarian, M.D., Dr.P.H.
Brigham and Women's Hospital, Boston, MA
dmozaffa@hsph.harvard.edu

Walter C. Willett, M.D., Dr.P.H.
Frank B. Hu, M.D., Ph.D.
Harvard School of Public Health, Boston, MA