��ɫ��Ƶ

The U.S. Department of Agriculture (USDA) has come under fire from politicians and potato lobbyists over its proposal to cut back on French fries and potatoes in school lunch and offer broccoli and other vegetables instead. Yet its plan is based on sound science—and could help turn around this country’s obesity and diabetes epidemics.

The USDA’s proposal is a straightforward switch: Cap the amount of potatoes and other starchy vegetables that school lunch can serve at one cup per week—the equivalent of a medium baked potato—and promote a wider variety of vegetables, especially dark green and orange varieties, such as broccoli, spinach, and carrots. (1) The recommendation is part of a 76-page proposed overhaul of the nutrition standards in U.S. school meal programs, and the agency is on solid scientific footing: It’s following the recommendations from an expert panel at the Institute of Medicine (IOM), which spent a year reviewing research on children’s nutrient needs, as well as food choices that prevent obesity and chronic disease. (2)

U.S. children, on average, only eat about 40 percent of the government’s daily recommended vegetable intake—and 29 percent of that comes from potatoes, most of them fried. (2) Children are especially low in their intake of dark green vegetables, orange vegetables, and legumes (dried beans), getting less than 20 percent of the recommended intake.

By limiting starchy vegetables at lunch, and setting new requirements for dark green and orange vegetables, the IOM was trying to steer children’s diets in a healthier direction: “The committee anticipates that…with repeated exposures and high-quality food preparation, students will learn to value the vegetable items offered.” (2, p. 170) In other words, over time, kids will get used to eating broccoli, carrots, and other colorful vegetables—and may even start to like them.

Potatoes don’t count as a vegetable on Harvard’s new Healthy Eating Plate, and with good reason: They are very high in carbohydrate—in particular, the kind of carbohydrate that the body digests rapidly, causing blood sugar and insulin to surge and then dip. (The scientific term for this is that they have a high glycemic load.)  In the short term, this roller coaster-like effect on blood sugar and insulin can lead people to feel hungry again, soon after eating—and this, in turn, can lead to overeating. (3) Over the long term, diets high in potatoes and similarly rapidly-digested, high carbohydrate foods can contribute to obesity, diabetes, and heart disease. (4–9)

Potatoes do contain important nutrients—vitamin C, potassium, and vitamin B6, to name a few. But the potato is not the only source of these nutrients, nor is it the best: Cup for cup, for example, broccoli has nearly nine times as much vitamin C as a potato, and white beans have about double the potassium. Yet a cup of potatoes has a similar effect on blood sugar as a can of Coca Cola or a handful of jelly beans. (10) That’s a high metabolic price to pay for nutrients that children can easily get from other sources.

Potatoes seem to be a particular culprit for weight gain and diabetes. A recent study from Harvard School of Public Health that tracked the diet and lifestyle habits of 120,000 men and women for up to 20 years looked at how small food-choice changes contributed to weight gain over time. People who increased their consumption of French fries and baked or mashed potatoes gained more weight over time—an extra 3.4 and 1.3 pounds every four years, respectively. (6) People who decreased their intake of these foods gained less weight, as did people who increased their intake of other vegetables. A similar long-term study found that high potato and French fry intakes were linked to a greater risk of diabetes in women, and that replacing potatoes with whole grains could lower diabetes risk. (5)

For people who are lean and active, potatoes likely don’t exact such a severe metabolic toll. But one out of three children and two out of three adults in the U.S. are overweight or obese, and many do not get enough daily physical activity. That’s all the more reason to use potatoes sparingly in our meals, if at all.

“Eating more than two servings of potatoes a week may be okay for people who dig their own,” says Walter Willett, Professor of Epidemiology and ��ɫ��Ƶ and chair of the Department of ��ɫ��Ƶ at HSPH. “But today, few Americans get the amount of physical activity our ancestors did 80 years ago, and that means our metabolism responds poorly to high amounts of starch.”

Some politicians and potato lobbyists have raised concerns that replacing potatoes with a wider variety of vegetables would add $6.8 billion to the cost of school lunches over the next five years. (11) But that appears to be a short-sighted point of view: Obesity costs this country an estimated $152 billion a year in healthcare expenses, and those could rise to an estimated $319 billion by 2020. (12) That makes the cost of this school lunch upgrade seem like just a drop in the potato bucket.

References

1.U.S. Department of Agriculture. ��ɫ��Ƶ Standards in the National School Lunch and School Breakfast Programs: A Proposed Rule by the Food and ��ɫ��Ƶ Service on 01/13/2011. . 2011;76:2494–2570.

1. Institute of Medicine. . Washington, D.C.: National Academies Press; 2009.

2. Abete I, Astrup A, Martinez JA, Thorsdottir I, Zulet MA. Obesity and the metabolic syndrome: role of different dietary macronutrient distribution patterns and specific nutritional components on weight loss and maintenance. . 2010;68:214-31.

3. Halton TL, Willett WC, Liu S, et al. Low-carbohydrate-diet score and the risk of coronary heart disease in women. . 2006;355:1991-2002.

4. Halton TL, Willett WC, Liu S, Manson JE, Stampfer MJ, Hu FB. Potato and french fry consumption and risk of type 2 diabetes in women. . 2006;83:284-90.

5. Mozaffarian D, Hao T, Rimm EB, Willett WC, Hu FB. Changes in diet and lifestyle and long-term weight gain in women and men. . 2011;364:2392-404.

6. Barclay AW, Petocz P, McMillan-Price J, et al. Glycemic index, glycemic load, and chronic disease risk–a meta-analysis of observational studies. . 2008;87:627-37.

7. Beulens JW, de Bruijne LM, Stolk RP, et al. High dietary glycemic load and glycemic index increase risk of cardiovascular disease among middle-aged women: a population-based follow-up study. . 2007;50:14-21.

8. Chiu CJ, Liu S, Willett WC, et al. Informing food choices and health outcomes by use of the dietary glycemic index. . 2011;69:231-42.

9. The University of Sydney. . Accessed October 8, 2011.

10. Huang, J. USDA wants to limit potatoes in school lunches. . October 5, 2011.

11. Dor AF, Langwith C, Tan E. A heavy burden: The individual costs of being overweight and obese in the United States. The George Washington University School of Public Health and Health Services Department of Health Policy, 2010.