Gestational diabetes -- hyperglycemia during pregnancy -- effects a considerable number of women. It is also a known risk factor for developing diabetes (T2) later in life. Some degree of peripheral insulin resistance normally develops during pregnancy. Why? Because the fetus' growth and development takes priority in nutrient partitioning so glucose is conserved for the fetus much like it is conserved for the brain in the fasted/starved/glucose-deprived state. The link of GD to T2 most likely reveals the genetic predisposition towards IR -- in other words, while diet can cause insulin resistance, there is a genetic component in most who eventually develop hyperglycemia as a result. Most women will compensate for the mild IR state and maintain normal glycemia during pregnancy, while those who are perhaps even mildly IR to begin with will exceed their capacity to compensate during the pregnancy. In most cases, deliver the baby and the diabetes goes away.
This study used data from the Nurses Health Study II, which began tracking female nurses in the US in 1989 (age range in '89 22-44 y.o.a.). This particular study included women who reported a single pregnancy that lasted at least 6 months (between 1991 and 2001) numbering 13,475. There were 860 cases of GD (6.4%) reported. They looked at dietary intake data collected (from periodic self reported intake*) and analyzed it for the total fat content as well as content of classes of fats (SFA, MUFA, PUFA) etc.
In multivariate models, total fat, fat subtypes, and the source of fats (animal compared with vegetable fat) were expressed as the nutrient density (percentage of calories from fat) and modeled as quintiles of intake. Quintiles were deﬁned by the distribution of each nutrient at baseline.Quintiles divide the sample into 5 groups of equal numbers of subjects. The lowest quintile was used as the reference for determining risk ratios (RR). Here's the baseline data -- you can click to enlarge
Risk Ratios for Total Fat, Animal Fat and Veggie Fat
Risk Ratios for Classes of Fats
RR1: Adjusted for Age (5yr increment) and BMIRR2: Additionally adjusted for parity, physical activity, energy intake, smoking & alcohol intake and diabetes historyRR3: Additionally adjusted for cereal fibers, glycemic load and other fats
Now, let's keep in mind the limitations of these types of studies. Also, as LCHF advocates are always quick to point out, this fat intake is in the context of the SAD. Still, my reason for sharing this is that it is somewhat surprising given what we keep hearing about veggie oils and the glories of sat fats and fat consumption. I doubt these can be predictive at all for the LCHF diet, but some of the numbers really stand out to me. I'll summarize those below -- focusing on the number of cases per quintile and comparing lowest (Quint1) to highest quintile (Quint5)
- SFA: 133 cases in Quint1 vs. 196 cases in Quint5
- MUFA: 145 cases in Quint1 vs. 173 cases in Quint5
- PUFA: 173 cases in Quint1 vs. 140 cases in Quint5
- PUFA/SFA ratio: 216 cases in Quint1 vs. 122 cases in Quint5
That GD incidence increased significantly with SFA intake, and decreased significantly with PUFA intake is the sort of data that flies in the face of this notion that veggie oils are to blame for the increased incidence of diabetes in general, and tends to implicate SFA's. That ratio of PUFA/SFA is rather striking and stood out to me.
- Animal Fat: 125 cases in Quint1 vs. 230 cases in Quint5
- Veggie Fat: 200 cases in Quint1 vs. 144 cases in Quint5
I would also make note of the fact that the glycemic loads were actually lower in the higher fat quintiles. The carb intake in the animal fat quintiles went from 58% of energy to 43% of energy from Quint1 to Quint5, and from 53% to 48% in the veggie fat group.
I'm not going to be microanalyzing this data, certainly there are some things one can pull out to explain the data that counters any dearly held beliefs. If anyone wants the full text of this for your own reference, shoot me an email (carbsane at gmail dot com). I just came across this looking for something else, as often happens, but the results were surprising enough that I thought I'd share them with you.