Download Dietary Fiber and Weight Gain

Dietary Fiber and Weight Gain
JAMA, The Journal of the American Medical Association, April 12, 2000 v283 i14 p1821.
Mark F. McCarty, Robert J.L. Waugh, David S. Ludwig, Mark A. Pereira and David R. Jacobs Jr.
To the Editor: The study by Dr Ludwig and colleagues [1] provides evidence that a high intake
of low-fiber foods is a key mediator of the epidemic of obesity in the United States. The authors
plausibly suggest that this effect is primarily attributable to the often-high glycemic index of
such foods. A secondary but no less intriguing finding of their study is that increased protein
intake is linked to weight gain. The 2 findings may share a common mechanism.
Although dietary protein, administered alone, has a relatively modest impact on insulin secretion,
it can markedly potentiate the insulin response to coingested starch. [2] Remer et al [3] reported
that when 32 g/d of egg protein was added to a low-protein lactovegetarian diet, the level of C
peptide in 24-hour urine, thought to be roughly proportional to diurnal insulin secretion,
increased by 60%. Another study compared the bariatric effects of 2 isocaloric low-energy diets
of identical macronutrient composition--1 of which was a "low-insulin-response" regimen,
emphasizing lower-glycemic-index starches and banning the coingestion of starch and animal
protein; not surprisingly, weight loss was significantly greater with this regimen. [4] These
considerations may be relevant to the characteristic leanness of vegans, who typically eat large
amounts of fiber-rich whole foods and avoid animal protein. The findings of Ludwig et al may
be viewed as support for the proposition that a whole-food vegan diet--in addition to its
numerous other health-protective attributes--is an effective strategy for maintaining leanness.
Consider the typical, popular "fast food" meal--a slab of animal protein wedged between white
flour buns and complemented with french fries and a sugary drink. This is an ideal strategy for
achieving the maximal postprandial surge in insulin. More generally, US meals often juxtapose
animal protein with high-glycemic-index starch. Wheat flour products may contribute notably to
obesity--the insulin response to wheat flour (with the exception of pasta) is as high as that
evoked by pure glucose, in part because the protein content of wheat is relatively high.
The failure of percentage of dietary fat to influence body weight in the analysis by Ludwig et al
does not rule out the possibility that the very low fat content (approximately 10%) of quasivegan diets contributes to the substantial "spontaneous" weight loss often seen with these
regimens. [5] Especially when combined with daily exercise, such diets often lead to marked
improvements in muscle insulin sensitivity that induce a compensatory down-regulation of
insulin secretion. [6]
Mark F. McCarty
Pantox Laboratories
San Diego, Calif
(1.) Ludwig DS, Pereira MA, Kroenke CH, et al. Dietary fiber, weight gain, and cardiovascular
disease risk factors in young adults. JAMA. 1999;282:1539-1546.
(2.) Rabinowitz D, Merimee TJ, Maffezzoli R, Burgess JA. Patterns of hormonal release after
glucose, protein, and glucose plus protein. Lancet. 1966;2:454-456.
(3.) Remer T, Pietrzik K, Manz F. A moderate increase in daily protein intake causing an
enhanced endogenous insulin secretion does not alter circulating levels or urinary excretion of
dehydroepiandrosterone sulfate. Metabolism. 1996;45:1483-1486.
(4.) Slabber M, Barnard HC, Kuyl JM, et al. Effects of a low-insulin-response, energy-restricted
diet on weight loss and plasma insulin concentrations in hyperinsulinemic obese females. Am J
Clin Nutr. 1994;60:48-53.
(5.) Ornish D, Brown SE, Scherwitz LW, et al. Can lifestyle changes reverse coronary heart
disease? the Lifestyle Heart Trial. Lancet. 1990;336:129-133.
(6.) Barnard RJ, Ugianskis EJ, Martin DA, Inkeles SB. Role of diet and exercise in the
management of hyperinsulinemia and associated atherosclerotic risk factors. Am J Cardiol.
1992;69:440-444.
To the Editor: Certain key information would be helpful in considering the practical application
of the findings reported by Dr Ludwig and colleagues. [1] Although the authors indicate that "a
relatively large spread was observed in dietary fiber intake among individuals," the study did not
examine the effect of fiber type, source, or form. It would be informative if Ludwig et al could
supply the information about the average actual dietary fiber intake in grams per day in each of
the 4 groups, the average dietary fiber intake in grams per day in the (unpublished) median
quintile group, and a description of the average "typical" food intake per day in the highest
quintile group.
Robert J. L. Waugh, MD
New York, NY
(1.) Ludwig DS, Pereira MA, Kroenke CH, et al. Dietary fiber, weight gain, and cardiovascular
disease risk factors in young adults. JAMA. 1999;282:1539-1546,
In Reply: Mr McCarty raises an interesting point regarding the effect of dietary protein on body
weight. Our study suggests that diets low in fiber may increase the risk of obesity and heart
disease by raising insulin levels. McCarty notes that protein potentiates the insulin response to
carbohydrate and may therefore promote weight gain. In support of this supposition, we did find
that protein consumption was modestly associated with body weight and several cardiovascular
disease risk factors. However, recent findings from the Nurses' Health Study suggest that dietary
protein actually may protect against ischemic heart disease. [1] The effects of protein on
hyperinsulinemiarelated health outcomes could be influenced by several factors: protein source
(animal proteins have a higher lysine-to-arginine ratio than vegetable proteins and, for this
reason, stimulate more insulin secretion [2]) dietary patterns (increased secretion of insulin
would be expected if dietary protein replaced fat or low-glycemic-index carbohydrate, but not if
protein replaced high-glycemic-index carbohydrate; eg, postprandial insulin levels were lower
after consumption of high-protein foods vs equicaloric portions of many high-carbohydrate foods
[3]), and noninsulin-mediated actions (protein may be more satiating than the other
macronutrients, [4] possibly because of effects on glucagon secretion).
We agree with McCarty's second point: our analyses do not rule out the possibility that very lowfat diets may produce weight loss. However, the weight loss reportedly obtained in a study by
Ornish et al [5] cannot be attributed specifically to reductions in dietary fat, because their
approach also includes many behavioral modifications. Additional research is needed to
determine the optimal macronutrient ratio, if one exists, for prevention and treatment of obesity
and heart disease. The additional information requested by Dr Waugh is presented in the
TABLE.
David S. Ludwig, MD, PhD
Mark A. Pereira, PhD
Children's Hospital Boston, Mass
David R. Jacobs, Jr, PhD
University of Minnesota Minneapolis
(1.) Hu FB, Stampfer MJ, Manson JE, et al. Dietary protein and risk of ischemic heart disease in
women. Am J Clin Nutr. 1999;70:221-227.
(2.) Sanchez A, Hubbard RW, Hilton GF. Hypocholesterolemic amino acids and the insulin
glucagon ratio. In: Sugano M, Beynen AC, eds. Dietary Proteins, Cholesterol Metabolism and
Atherosclerosis. Basel, Switzerland: Karger; 1990:126-138.
(3.) Holt SH, Miller JC, Petocz P. An insulin index of foods: the insulin demand generated by
1000-kJ portions of common foods. Am J Clin Nutr. 1997;66:1264-1276.
(4.) Stubbs RJ. Macronutrient effects on appetite. Int J Obes Relat Metab Disord. 1995;19(suppl
5):S11-S19.
(5.) Ornish D, Brown SE, Scherwitz LW, et al. Can lifestyle changes reverse coronary heart
disease? the Lifestyle Heart Trial. Lancet. 1990;336:129-133.
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