Gestational diabetes: higher animal protein intake during pregnancy is associated with increased risk, and higher vegetable protein intake with decreased risk
- Discipline of Obstetrics and Gynaecology, Robinson Institute, The University of Adelaide, Adelaide, Australia
- Correspondence to: Ms Philippa Middleton, Department of Obstetrics and Gynaecology, Robinson Institute, The University of Adelaide, Adelaide, SA 5005 Australia;
Implications for practice and research
Pregnant women or women planning to become pregnant may benefit from substituting some animal protein with vegetable protein (including nuts) and perhaps replacing some red meat with fish and poultry.
Midwives can incorporate this nutritional advice into prenatal care.
The role of advanced glycation end products and influence on diabetes risk is a research priority.
Intervention studies are required to assess the effects of reducing and substituting some forms of meat before and during pregnancy.
Gestational diabetes mellitus (GDM) can result in significant adverse outcomes for mother and child, both in the short-term and long-term and is increasing in prevalence in many parts of the world. Understanding more about the influence of dietary and lifestyle choices on GDM will help us to know how to modify dietary intake, such as type of protein, to prevent GDM and stop or delay progression to type 2 diabetes.
This cohort study, examining the links between dietary protein prior to pregnancy and GDM, originates from the US Nurses’ Health Study II. Eligible women were those reporting at least one singleton pregnancy between 1991 and 2001. Information such as BMI and self-reported GDM was reported by biennial questionnaires, with food intakes reported every 4 years, although diet during pregnancy was not assessed. Analyses were adjusted for factors including maternal age, BMI and physical activity.
In this cohort of 15 294 women (21 457 pregnancies), there were 870 incident GDM pregnancies. An increased risk ratio (RR) of GDM was found with higher intake of animal protein pre-pregnancy (adjusted RR=1.49, 95% CI 1.03 to 2.17; p=0.013), while there was a decreased risk of GDM for higher pre-pregnancy intake of vegetable protein (adjusted RR=0.69, 95% CI 0.50 to 0.97; p=0.034). For animal protein, the risks were significant for unprocessed and processed red meat and red meat in total, but not for fish or poultry. Just over half a serving of nuts a day was associated with 40% reduction in risk of GDM.
An earlier study, also using data from the US Nurses’ Health Study, showed that high pre-pregnancy intake of dietary haeme iron (mainly from animal meat) was associated with an increased risk of GDM.1 Another prospective study has found an association between high dietary haeme (in the preconception and early pregnancy period) and GDM.2
There are also several reports linking red meat consumption and increased risk of type 2 diabetes.3 One of the latest is a combined Health Professionals and Nurses Study analysis of changes in diet, indicating that higher consumption over time increases type 2 diabetes risk.4
So there seems to be increasing evidence for red meat being implicated in an elevated risk of GDM and type 2 diabetes. Is it the ‘red’ in red meat, leading to oxidative stress from high dietary iron intake? There may be just as much iron (in the form of myoglobin) in some poultry and fish, so proinflammatory mechanisms related to high fat content, particularly for processed meat, have also been proposed.5 Perhaps the additives and preservatives in processed meats such as sodium nitrate might play a role in increased risk of diabetes. Advanced glycation end products could be another culprit. These are related to processed and fresh meat, and are implicated in inflammation as well as oxidative stress, through storage and high-temperature cooking.3
What does this mean for pregnant women and women contemplating pregnancy? It may be prudent to consume lean fresh meat and avoid processed meats and meats cooked at high temperatures, and as long as iron stores are adequate, to substitute some animal protein with vegetable protein. Although the associations with diabetes seem robust, the mechanisms remain unclear. We need further elucidation to refine our knowledge of how to adapt women's diets and other lifestyle behaviours to prevent both gestational and type 2 diabetes.
Competing interests Part of Philippa Middleton's research involves assessing interventions for preventing and treating gestational and type 2 diabetes.