Reply to SN Gershoff

¹ Department of Human Studies Clinical Nutrition Research Center University of Alabama at Birmingham Birmingham, AL 25294
² Department of Nutrition Sciences Clinical Nutrition Research Center University of Alabama at Birmingham Birmingham, AL 25294 E-mail: weinsier{at}shrp.uab.edu
³ Department of Nutrition Sciences University of Alabama at Birmingham Birmingham, AL 25294

Dear Sir:

We thank Gershoff for his kind words concerning our recent article in the Journal (1). We agree with the editorial comments of Wyatt and Hill (2) that it is possible that weight-reduced persons may have to exert more effort to maintain weight than do never-overweight persons. It is impossible to know whether this is due to an increased drive to eat, lower physical activity, or some metabolic factor such as enhanced lipogenesis, as proposed by Gershoff.

It does seem plausible that lipogenic enzymes may be upregulated in response to a loss of stored fat, as previously reported by Huber et al (3). It is well known that up-regulation of glycogen synthase occurs in skeletal muscle after the glycogen-depletion phase of glycogen supercompensation. We also observed supercompensation in muscle lipid storage after depletion of lipid in muscle induced by 2 h of running (4). However, this supercompensation only occurred when the euenergetic diet included 35% of energy as fat, so it is impossible to know whether lipid depletion, a moderately high-fat diet, or a combination of both factors were responsible for the lipid supercompensation.

We should point out that in our study comparing "gainers" and "maintainers" (1), no differences in fuel utilization (as reflected by fasting and 24-h respiratory quotients) or resting energy expenditure were found. This finding suggests that the differences in weight-gain patterns were probably based on behavior, expressed as increased energy intake, decreased activity-related energy expenditure, or both. In fact, the difference in activity-related energy expenditure between the gainers and maintainers over the 1 y after follow-up accounted for most of the observed weight gain in the gainers.

It is difficult to see how differences in fat tissue lipogenesis could cause weight gain in persons who are not in positive energy balance. However, it is possible that persons with an up-regulation of lipogenic enzymes may also have an increased appetite, perhaps through some feedback system originating in fat cells.

In conclusion, we believe that our data support the notion that much of the gain in body weight occurs because of decreased physical activity, increased energy intake, or both. If, in fact, metabolic or physiologic differences exist between gainers and maintainers, the role that these differences play are likely to be largely expressed through behavior.

REFERENCES

1. Weinsier RL, Hunter GR, Desmond RA, Byrne NM, Zuckerman PA, Darnell BE. Free-living activity energy expenditure in women successful and unsuccessful at maintaining a normal body weight. Am J Clin Nutr 2002;75:499–504.
2. Wyatt HR, Hill JO. Let’s get serious about promoting physical activity. Am J Clin Nutr 2002;75:449–50.
3. Huber AM, Gershoff SN, Antoniades HN. The effect of fasting and refeeding on isolated rat adipose tissue activity in the presence of crystalline and "bound" insulin. Metabolism 1965;14:619–24.
4. Larson-Meyer DE, Newcomer BR, Hunter GR. Influence of endurance running and recovery diet on intramyocellular lipid content in women: a ¹H NMR study. Am J Physiol Endocrinol Metab 2002;282:E95–106.