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The Center for Public Health Nutrition
305 Raitt Hall #353410
University of Washington
Seattle, WA 98195-3410
E-mail: adamdrew{at}u.washington.edu
Institut National de Recherche Agronomique (INRA)
Centre de Recherche en Nutrition Humaine (CRNH)–Ile de France
INSERM U557, INRA U1125, CNAM EA3200
Univ Paris 13
Bobigny F-93017
France
Dear Sir:
We thank Dr Estep for agreeing with our position (1) that liquid meal replacements (MRs) can promote both satiety and weight loss. Not everyone, however, shares our point of view. Our colleague, Dr Mattes, has recently argued (2) that the success of MRs in promoting weight loss is unrelated to physiologic satiety. Instead, he suggested that, because of their weak satiety value, liquid MR products were widely consumed for the purpose of weight gain (3).
The notion that successful weight control depends on how the products are used was the second major premise of our review. We pointed out that MR shakes are consumed instead of meals, whereas caloric beverages are consumed with or between meals (1). We also suggested that dietary behavior rather than the metabolic response to sugar was the principal factor responsible for weight change. After all, the sugar content of soft drinks, fruit juices, flavored milks, and MR shakes is approximately the same (1).
Estep now makes the additional point that, in contrast to most caloric beverages, MR shakes necessarily contain protein, fat, and fiber. These nutrients may not only induce but also prolong satiety (1). He further describes the amounts of protein and fiber in MR shakes as average to "very high." That is not exactly correct. MR shakes are frequently sold in cans containing 11 fluid ounces (325 mL). One typical MR product, currently available on the market, contains (per 1-can serving) 9 g protein, 4 g fiber, and 1.5 g fat. For comparison purposes, 11 fl oz of low-fat milk (1% fat) contains 11 g protein and 3.5 g fat. In other words, MR shakes contain less protein than can be obtained from an equivalent amount of low-fat milk.
Protein does promote satiety, but its effects may be threshold dependent. Studies from 2 separate laboratories have failed to observe differences in satiety profiles between 1%-fat milk, orange juice, and cola beverages. In one study (4), beverage preloads were consumed some time before the test meal; in the other (5), they were consumed with the meal. No differences in hunger, fullness, or energy intakes were observed. In contrast, the consumption of more viscous yogurts (14 g protein/325 mL) led to higher fullness ratings than were observed for fruit and milk-based beverages of equal caloric value (6).
Studies on the effect of soluble fiber in beverages on satiety are very limited, as we pointed out in our review (1). Most of that work has been done on solid and semi-solid foods. Again, it is important to keep the amounts in perspective. MR shakes contain approximately the same amount of fiber as is found in an equivalent amount of canned prune juice (3.3 g). There may well be a synergy between low amounts of protein and fiber in liquid food systems in their effect on satiety; however, such data are not publicly available at this time.
Estep's next argument is more complicated. First, he speculates that 2 of the published MR trials may have included a large proportion of patients who were lactose intolerant. However, lactose intolerance was not mentioned by the original authors. No subjects in the first study withdrew because serious adverse side effects (7). In the second study, 7 of 100 patients experienced transient abdominal discomfort of unknown origin (8). Other studies we reviewed made no mention of this issue.
Estep then argues that the participants' failure to absorb lactose may have increased the proportion of calories from protein in MR shakes to 39% of total energy, which he describes as "triple the typical protein intake" in the usual Western diet. However, such comparisons are meaningful only if the percentages are calculated with the use of the same denominator. Whereas the proportion of protein energy in the Western diet (11–14% of energy) is generally based on 2000 kcal (65g protein/d), the proportion of protein energy in MR shakes seems to have been based on 220 kcal. The absolute amount of protein per can (9 g) was the same whether lactose was absorbed or not.
In summary, MR shakes contain less protein than does low-fat (1%) milk and slightly more fiber than does prune juice. They also contain up to 45 g carbohydrates, including 34 g sugars. That they still are capable of promoting weight loss suggests that dietary behavior, not sugar biochemistry, is the critical component of weight loss—or weight gain.
ACKNOWLEDGMENTS
Both authors have received past and current research funding from US and international food companies and industry associations. Neither author has any ties to manufacturers of meal replacement products. Neither of the authors had a personal or financial conflict of interest.
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