The Effect of Weight Loss in Overweight, Lactating Women on the Growth of Their Infants
ABSTRACT & COMMENTARY
Synopsis: Weight loss of approximately 1 lb per week in lactating women does not affect infant growth during the first three months.
Source: Lovelady CA, et al. N Engl J Med 2000;342: 449-453.
For many years, it has been suggested that planned weight loss can occur during lactation without fear of injury to the mother or infant. Despite the fact that this recommendation is made by many clinicians and various bodies that make policy statements, no randomized trial has previously been conducted.
Lovelady and colleagues recruited postpartum, lactating women into this study who were generally healthy except for a body mass index (BMI) of 25-30. In addition, the women were required to have a sedentary lifestyle, be nonsmoking, and exclusively breastfeeding. The offspring had to have been delivered vaginally at term, with a weight of at least 2500 g. Women who agreed to participate in the study had extensive baseline measurements before random assignment to either a diet and exercise group or a control group. Baseline measurements included standard height and weight, skinfold thickness measurements at six body sites, residual lung/volume measurement, and body density calculations. In addition, the women were required to use portable digital scales to measure all solid and liquid intake for three consecutive days at baseline (4 weeks postpartum), at midstudy (9 weeks postpartum), and at study conclusion (14 weeks postpartum). The cardiovascular fitness of each woman was estimated using a standard methodology. Caloric intake during the study was individually assigned, with the study group receiving 500 kcal less intake per day than the control group. The exercise program required four 45-minute sessions of aerobic exercise. Those women who were not fit at the beginning of the study exercised 15 minutes initially and increased the length by two minutes each day until they could safely exercise for 45 minutes.
Forty-eight women enrolled in the study. Twenty-seven were assigned to the diet and exercise program, and 21 to the control group. Eight women dropped out of the study—six in the diet and exercise group and two in the control group. The control and study groups were similar based on a number of demographic factors. However, the women who dropped out of the study were significantly heavier than those women who remained in the study.
During the 10 weeks of the study, the diet and exercise group lost an average of 4.8 kg (10.5 lb). The control group lost an average of 0.8 kg (1.8 lb). This difference was significant. There were no differences in the weight gain of the infants in either group. The average weight gain in both groups was similar to that recorded in other studies.
Lovelady et al conclude that "moderate weight loss" (approximately 1 lb/wk) in lactating women has no effect on infant growth.
Comment by Kenneth L. Noller, MD
Obesity remains one of the major challenges in health care today. While cardiovascular disease has been reduced in the population overall, the percentage of individuals who are overweight continues to rise. According to a recent study quoted by Lovelady et al, 51% of women in the United States have a BMI greater than 25.
There are a few times in our lives when losing weight seems easier than others. For many women, the period of lactation is such an opportunity. Milk production requires 500-800 kcal per day. In addition, the new mother is usually extremely active, particularly if she has other young children to care for. Even moderate calorie restriction during lactation can result in impressive weight loss.
But how safe is it for a lactating woman to attempt to lose weight? This study suggests that such attempts are safe both for the mother and for her infant. However, there are some problems with generalizing this study. The study groups were extremely small. Heavier patients tended to drop out of the study. Lovelady et al did not determine whether weight loss of 1 lb/wk achieved purely by calorie restriction without exercise was similarly safe for mother and infant. Nonetheless, we can be relatively reassured when we suggest to our patients that lactation is an excellent time for weight loss.
As an aside, you might have noticed that I detailed the study methodology in my summary of the article more than usual. I did this on purpose to emphasize the fact that performance of weight loss studies has become an extremely complicated task. Simple measurement of weekly weight is no longer considered to be a valid study design.
According to the study by Lovelady et al, which of the following is true concerning lactating women?
a. Weight loss of approximately 1 lb/wk is safe for mother and infant.
b. Weight loss of 1 lb/wk is safe for the mother but results in poor infant growth.
c. Postpartum weight loss is safe for women who have delivered vaginally but not for women who have undergone cesarean delivery.
d. Maternal weight loss of 1 lb/wk is safe only for infants weighing more than 2500 g at birth.
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