Pregnant and lactating women form a vulnerable group in whom the effects of low protein intakes may manifest themselves in various ways: the normal increase in body-weight may be considerably reduced; complications of pregnancy such as miscarriage, stillbirth or premature birth are more frequent. There are also many studies showing that nutrition of a woman during pregnancy can affect the health of her baby for its lifetime, notably the the susceptibility of adults to infections as well as chronic diseases.
Although mothers on relatively poor diets seem able to provide sufficient milk for their children, this may have debilitating long-term consequences for the woman, as she is forced to consume her own body reserves. The total protein content and amino-acid composition of milk from malnourished mothers are not significantly different from well-nourished mothers, with the result that the extra protein requirement must be at the expense of the mothers' tissues. For example, in India lactating women were found to have an average deficit of two grams of protein per day. Women with very inadequate diets or frank malnutrition, have a reduced milk volume, and the energy content of the milk may be lowered by a decline in the lipid constituents. The protein and carbohydrate components of the milk appear to be relatively unaffected, even in extreme cases, though the concentrations of some vitamins may be significantly decreased. The poor milk supply associated with maternal malnutrition can in turn lead to unsatisfactory infant nutrition, especially among the low-birth-weight babies who need to compensate for inadequate intrauterine growth. There is, therefore, a link between maternal malnutrition and subsequent malnutrition in the offspring.
In affluent societies most women have an adequate diet and sufficient nutritional stores to compensate for the increased demands of breast feeding, but in poorer societies this is often not the case. In developing countries, women are subjected to a variety of nutritional stresses caused by inadequate diets, the demands of recurrent pregnancy and lactation associated with high fertility, the energy requirements of hard physical work, the adverse nutritional effects of infection and parasitic diseases, and traditional customs which proscribe certain foods or lead to an unequal distribution of food within the family. All these factors interact and produce a 'continuous, cumulative nutritional drain', which has been described as the 'maternal depletion syndrome'. Lactation plays an important role in the genesis of this chronic maternal under-nutrition, and in extreme cases lactation may even precipitate frank malnutrition. Furthermore, these poorly nourished mothers tend to have low birth weight infants who suffer from an increased risk of morbidity and mortality.
A study (reported in 2001) linked the birth months of more than a million people who died in Denmark and Austria after the age of 50. Adults who were born in Austria in the autumn (between October and December) lived about 0.6 years longer than those born in the spring (April to June). In Denmark, the difference was 0.3 years. There was a "mirror image reversal" for people born in Australia, where the difference was 0.35 years in favour of those born in the autumn (which in the southern hemisphere is April to June). The possible relationship with nutrition during pregnancy is that more fruits and vegetables are available during the summer and autumn months than during the winter and spring months. This means that a woman pregnant during the summer and fall could have a better food selection and their babies would be larger and healthier.
Haiti is the poorest country in the Western Hemisphere, with 80% of its people living below the poverty threshold. As a result of this extreme poverty, each year almost 50,000 pregnant and nursing women and children under age five suffer from moderate and severe malnutrition and anaemia.