Pregnancy. Pregnancy and body weight increases are intertwined in a complicated pattern. Female fat stores have a primary function to provide energy for pregnancy and lactation. A pregnant woman requires approximately 130 000 kcal extra as the metabolic cost of pregnancy. Women who tend to put on too much fat in the early stages of pregnancy have been shown to keep this longer than those who do not put on excessive fat, or put on most fat later in the pregnancy. The recommended weight gain during pregnancy by the US medical specialists has risen from 7-Skg in the 1920s to 10-12kg in the 1970s. In 1989, the National Task Force on Prevention and Treatment of Obesity raised the recommendations to 14-16kg in 1995. However, there are now suggestions by some experts that this is too much and that the most recent recommendations are based simply on the modern average weight gain of pregnant women in the US. The previously recommended gain of 10-12kg has been suggested as a more appropriate health ideal for which to aim.

Breast-feeding is also known to be an effective form of fat burning, using up to 400kcal of energy per day. In one study carried out in the US, women who breast-fed for at least six months stayed leaner for up to two years than women who did not breast-feed at all or did so for less than six months. It has also been claimed that the risk of obesity increases with parity or the number of childbirths. This may be due to the repetitive exposure to the fat storing hormones of pregnancy, restrictions on physical activity or increased opportunity to eat more. In any case, for some women, pregnancy does appear to be a particularly high risk period for increases in obesity.

Research from the Stockholm Pregnancy and Weight Development Study in Sweden suggests that the greater the weight gain during pregnancy, the more likely the increase in post-partum body fat levels. Cessation of smoking with the onset of pregnancy may increase weight gain in the mother (although it certainly reduces the risk of birth complications in the baby). Those women who gained most weight during and after pregnancy were found to be those who had significantly changed their lifestyle from prepregnancy levels such as increased eating/snack eating and decreased levels of physical activity. Maintenance of physical activity through pregnancy and attention to nutrition, therefore, are most important to ensure a return to normal fat levels, but there are also special considerations for exercise which need to be considered. These are now available from most Health Departments.

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