Carb restriction ‘associated with T2D in Australian women’

Executive summary
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Introduction

Many thanks to Dr Peter Brukner for this week’s topic. Peter is one of my main paper finders. He spotted an article, which was published in November 2019, based on women in his home country of Australia. The paper was called “Carbohydrate restriction in midlife is associated with higher risk of type 2 diabetes among Australian women: A cohort study” (Ref 1).

Some studies make no sense as soon as you see the title and this study was one of those. Since type 2 diabetes is a condition characterised by the inability to handle carbohydrate, it makes no sense that women who are restricting carbohydrate are at higher risk of type 2 diabetes (T2D henceforth).

The study

The Australian Longitudinal Study on Women’s Health is an ongoing population study of women in Australia. It is described as nationally representative. It started in 1996, when three cohorts of women were established: the young cohort (born 1973-78); the middle-aged cohort (born 1946-51); and the older cohort (born 1921-26). At the first survey in 1996, the women in these cohorts were aged 18-23, 45-50 and 70-75 years, respectively.

This particular paper looked at women from the 1946-51 cohort only. After the first survey (1996), women were resurveyed in 1998 (survey 2) and every three years thereafter until 2016 (surveys 3-8). The response rate was 90% for survey 2. It dropped in successive surveys until survey 8, which had a 63% response rate.

The dietary assessment was conducted in 2001 (when the women were aged 50-55) and in 2013 (aged 62-67). After eliminating participants with poor or missing dietary data, 9,689 women were included in this study.

Average long-term carbohydrate restriction was assessed using a low-carbohydrate diet score and placing the women into four groups (quartiles). The highest carb group (Q1) averaged 50% carbohydrate intake. The lowest carb group (Q4) averaged 37% carbohydrate intake. As with last Monday's note, this paper did not study low carb diets. However, at least this week's study referred to carbohydrate restriction, rather than claiming to have studied low carb diets.

Incidence of T2D developed between 2001 and 2016 was self-reported at 3-yearly surveys.