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There has been a tendency not to study the female body in science and medicine. Only since the 1990s, when it was made law in the US, have scientists been forced to include at least some women in their research (or show cause why not). It’s even worse for pregnancy…pregnant women are routinely excluded from just about any study. Reasons include ‘women’s bodies are too complicated, the menstrual cycle will interfere with results’.

Yet, when it comes to obesity and lifestyle research, women volunteer at twice the rate of men. We live longer lives too so there must be something we do right and it’s worth investigating why and how. We know we have a more active immune system which might serve us well most of the time. There is a hypothesis that because women give birth, the female immune system has evolved around this. But it can turn on us when things go wrong – autoimmune diseases are more common in females.

Pregnancy is interesting from the point of view of obesity research. In the space of 9 months, we gain an average of about 13.5 kg, but many women gain twice that. This is the fastest rate of weight gain in life, faster even than adolescent boys at their peak. And yet, in the first trimester we appear to eat no extra calories, and often consume less than normal because we feel nauseous. And we still don’t know why nausea and vomiting are so common. Luckily, the vast majority of babies turn out perfectly formed despite the lack of (or perhaps in spite of) less than ideal nutritional intake.

Pregant woman

Interestingly, research shows that women don’t eat much more than usual during the last trimester than they did in the first trimester. How can this be when we weigh much more and are gaining weight fast? In 2015, two of my students did some research to find out more. We undertook a systematic review and meta-analysis (the gold standard of research these days) to find studies that had documented food and energy intake from early to late pregnancy (1).

There were only 18 studies over the past 25 years that met strict inclusion criteria (extraordinary, really!). On average women gained 12.0 kg and yet reported only a small increment in energy intake (about 450 kJ, or 100 calories per day) that did not reach statistical significance. This is only half the amount of additional energy that is recommended by health authorities – 1000 kJ per day in the 3rd trimester. In fact, it’s possible that the recommendations do harm, by encouraging women to gain an excessive amount of weight and therefore deliver bigger babies, destined to be overweight children and young adults.

We also know that the extra demands in pregnancy mean that micronutrient requirements also increase. The most important of these are iron, folic acid and iodine, which are particularly critical for brain growth and intellectual development. Human babies are born with brains that are 3 times larger for their weight than our nearest relatives, chimpanzees. Indeed, it’s one of the reasons that childbirth can involve a difficult labour and the decision to use a C-section delivery.

Unfortunately, even with a perfectly healthy diet, it is challenging to reach the target intake of vitamins and minerals for pregnancy. For this reason, pregnant women are routinely recommended to take dietary supplements to ensure they get the amounts needed. Their cost, however, may discourage vulnerable women from buying them. ¬¬¬

This fact makes me rather sad and angry. All of us have the right to start life in the best environment possible. Ideally, the moment of conception takes place in a healthy body, receiving the full quota of micronutrients needed for rapid cell division and differentiation. Women planning pregnancy can be counselled to take dietary supplements immediately. But we also know that half of all pregnancies are not planned. So an embryo might start life on the wrong foot. Nothing obvious, but not optimal for the formation of the first tissues in the brain. The effects may not be known for years and may be quite subtle. For example, we know that sub-clinical iodine deficiency in parts of Australia may be responsible for lower NAPLAN scores in primary school (2).

In my view, this is totally unacceptable situation. In a prosperous, highly developed country, Australian women (and men) have the right to a food supply that serves their needs from day 1 of conception. If the normal food supply and a healthy diet don’t give us what we need, then there is a good argument for fortification of some foods to make it possible. Currently, iodine must be added to some bread, but not all breads, and certainly not to rice, a key staple food for many Australians.

Which brings me back to our opening paragraph. The needs of women in pregnancy should be well studied, not avoided. There is a good argument for making their requirements the standard requirement – the common denominator when we study the nutritional needs of a whole population.


  1. Jebeile H, Mijatovic J, Louie JCY, Prvan T, Brand-Miller JC. A systematic review and metaanalysis of energy intake and weight gain in pregnancy. American Journal of Obstetrics and Gynecology 2016. 
  2. Hynes KL, Otahal P, Hay I, Burgess JR. Mild Iodine Deficiency During Pregnancy Is Associated With Reduced Educational Outcomes in the Offspring: 9-Year Follow-up of the Gestational Iodine Cohort. The Journal of Clinical Endocrinology & Metabolism 2013.

Professor Jennie Brand-Miller      
Professor Jennie Brand-Miller holds a Personal Chair in Human Nutrition in the Charles Perkins Centre and the School of Life and Environmental Sciences, at the University of Sydney. She is recognised around the world for her work on carbohydrates and the glycemic index (or GI) of foods, with over 300 scientific publications. Her books about the glycemic index have been bestsellers and made the GI a household word.