WEIGHT AND SEX HORMONES IN WOMEN


OBJECTIF NUTRITION 86 (DECEMBER 2007)
by Prof. Patrick Ritz (Metabolic Disease and Internal Medicine Division, University Hospital of Angers).


At equal height and weight, women expend less energy than men. As a result, the intake of equal amounts of food leads to disparities in weight and the greater prevalence of obesity. Some stages in life are particularly critical. During perimenopause, women are more exposed to weight gain in the form of visceral fat mass, which has negative metabolic and cardiovascular consequences. During pregnancy, a time where the risk of weight gain is high, the consulting physician can take advantage of the regular visits of his/her patient to help change her food-related behaviour if so desired.

The two sexes prove to be unequal when it comes to weight regulation and energy expenditure. This can be seen from the greater prevalence of obesity in women, who are subject to the impact of hormones with various weight-modulating effects during their childbearing years, either naturally (puberty, menstruation cycle, pregnancy, menopause) or due to therapeutic usage (contraception, hormone replacement therapy).

SPECIFIC CHARACTERISTICS OF THE ENERGY METABOLISM OF WOMEN

Higher energy expenditure in children than in adults is also reflected between the sexes starting at puberty. Several theories have been formulated in an attempt to explain these differences:
• children have a higher relative organ mass than adults. Since organs have a more intense metabolic activity than the rest of the body, particularly muscles, the energy expenditure of children is higher;
• the proportion between organ mass and muscle mass also differs between the sexes. Muscle fibre composition is not the same depending on gender. Women have a higher proportion of type I fibres, with less intense metabolic activity.

Natural male androgens (testosterone) do not have a direct thermogenic effect (increase in energy expenditure), but they do increase muscle mass. As a result, short-term treatment (7 to 10 days) does not modify energy expenditure, while three-month treatment results in a 7% increase by boosting lean body mass by approximately 10%.

Natural androgens in women may have a thermogenic effect. Indeed, differences in plasma levels in androstenedione determine energy expenditure at rest, explaining a 4% variance. This effect is independent from variations in body composition and from concentrations in thyroid hormones. From one extreme concentration of androstenedione to another, a difference in energy expenditure equal to 217 calories a day can be observed.

PUBERTY

This period brings considerable changes in hormonal impregnation, body composition and behaviour. It corresponds to an important growth phase in terms of height and weight which is responsible for higher energy needs. Girls gain considerably more adipose tissue than boys. The relative proportion of muscle mass (with low metabolic activity) within lean body mass increases in relation to organ mass. Behavioural changes also have a significant impact on weight changes during puberty. At this time, children acquire their independence in terms of physical activity (deciding to have or not to have it) and nutrition (buying their own food and sweets, etc.). These behavioural changes are subject to notable cultural influences. As a result, changes in weight and body composition during puberty vary considerably from one individual to another.

Early sexual maturity is a proven predisposing factor for higher fat body mass during adolescence and a higher risk of obesity in adulthood. Early sexual maturity in teenagers inhibits their growth, resulting in lower than average adult height and thereby promoting high BMI.

PREMENSTRUAL TENSION

The menstrual cycle brings variations in female sex hormone concentrations. A thermogenic effect of progesterone was clearly demonstrated. Furthermore, body temperature increases in the second phase of the cycle, while energy expenditure proves to be higher in the luteal rather than the follicular phase. The difference is in the order of 100 calories per day with notable individual differences.

Increased food intake also accompanies the luteal phase in both healthy women and those suffering from premenstrual tension. The difference, 10% on average, varies between the extremes of a 3% and 38% rise in additional energy intake during the luteal phase. The traditional "craving" for carbohydrates has not been demonstrated. However, among women experiencing cravings for specific foods, this urge is more frequent and more pronounced during the luteal rather than the follicular phase. Women who are neither ovulating nor taking oral contraception show no signs of different food intake between the two phases of the menstrual cycle.

The balance between oestradiol and progesterone probably has an impact on food intake. Estrogens inhibit food intake while natural progesterone has no effect on it. This may not be true of synthetic progestins, especially medroxyprogesterone acetate, which is used as an appetite stimulant during certain cancer treatments. It is this relative atmosphere of inhibition produced by the effect of oestradiol in the luteal phase that promotes food intake.

PREGNANCY

Pregnancy or pregnancies are often quoted in consultations for obesity as the triggering event in weight gain. Recommendations concerning desired weight gain during pregnancy are founded on the lower mortality of mother and baby. The most recent recommendations are in accordance with BMI before pregnancy (Table 1).

Weight gain in the order of 7 to 8 kg during pregnancy corresponds to the weight of the foetus, the increased volume of organs and tissue (breasts, uterus, blood volume) and the placenta. This is also accompanied by an increase in fat mass of approximately 3 kg, resulting in a total weight gain of 10 to 12 kg. All additional weight increase consists of fat mass.

Most of the studies conducted present pregnancy as responsible for weight gain that lasts up to 12 months after childbirth. This weight gain is highly variable. Three studies with irreproachable methodology concluded that average weight gain 12 months after childbirth consisted of 0.4 to 3 kg. In Sweden, a longitudinal study on some 1,500 women recorded an average weight gain of 0.5 kg at 12 months. However, 1.5% of the women had gained more than 10 kg, 13% among them between 5 and 10 kg, and 56% between 0 and 5 kg. A certain number of risk factors was identified. The severity of weight gain during pregnancy, age, quitting smoking and high weight gain after a previous pregnancy were risk factors that have been positively associated with weight retention after childbirth. At the same time, breastfeeding and irregular mealtimes proved to be relatively protective against weight gain, although only to a small extent. In this study, initial weight gain, parity, previous oestrogen-progestin contraception, social and marital status and nutritional advice during pregnancy were not associated with weight variations 12 months after childbirth.

MENOPAUSE

The three to five years of menopause prove to be critical for weight gain in women. Perimenopause corresponds to a sudden or gradual loss of hormonal progesterone and later oestrogen secretion.

Average weight gain is moderate but varies considerably from one woman to another. Depending on the study, it ranges from 0.6 to 5 kg. It is therefore not very high but generally occurring within a short period of time.

Total and perivisceral fat mass increases in the course of the menopausal transition. A decrease in lean body and muscle mass is much more debatable.

The causes of this variation in weight are complex. Firstly, energy expenditure at rest drops by approximately 100 calories a day. This occurs on average at the age of 48 onwards. Secondly, physical activity is reduced during the perimenopausal period, accounting for an approximate 130-calorie decrease in daily energy expenditure. Furthermore, recent studies on castrated animals show increased food intake and diminished physical activity, which are corrected by estrogens. The energy balance becomes positive through the intake of inappropriate foods and reduced energy expenditure: possible loss of lean body mass, loss of the thermogenic effect of progesterone, and reduction in physical activity.

A FEW SPECIFIC SITUATIONS

Amenorrhea is a frequently although not constantly encountered clinical sign of anorexia nervosa. It reflects the close relationship between weight, the hormonal mediators of adipose tissue and the regulation of the ovarian function by the hypothalamus.

Polycystic ovaries syndrome is responsible for dysmenorrhoea and insulin resistance. The latter causes anomalies in the metabolism of carbohydrates and lipids, leading to excess visceral fat with excess weight predominantly in the abdominal area.

Sterility treatment has a complex relationship with weight. Obesity reduces fertility. Induction of ovulation is often preceded by weight loss that has been requested by the gynaecologist, while often quoted as a factor of weight gain among patients.

Conclusion

Over the course of a woman’s life, weight changes are often slow to take effect, reflecting the excess (although moderately so) intake of food.

Weight correction proves to be easier when required weight loss is minimal and occurs at an early stage. Regular but not excessive surveillance of weight is an important factor of prevention. Some stages of a woman’s life are critical given their association with weight gain. Providing patients with information helps implement proper surveillance and prevention, and even weight correction methods.

References