This study shows an inverse relation between IRS frequency and consumption of fish, dairy products, and grain. The strength of the relation increased when the consumptions of these types of food were simultaneously high. The probability of having an IRS was approximately five times lower when the consumption was above the median cut off point for fish, dairy products, and grain together, in comparison with a low consumption of all three types of food. The potential protective effect against IRS seems to be more effective for fish intake than for dairy products or grain consumption. However, an additive effect was present with a combination of these food groups. Comparative to fish intake, when the consumption of dairy products and grain increased (fifth quintile) the risk of developing an IRS tended to increase also, suggesting that a high consumption of these foods could have an opposite effect on insulin resistance. The negative association could be confounded by intakes of other foods and by healthy profiles. After adjustment for confounders, the inverse association between food and IRS remained significant. The lack of significant interaction between these food items and IRS may imply that the relation between food and IRS is not dependent either on the other two types of food studied in this population or on the amount consumed in particular. Moreover, when the consumption of fish increased, the probability of having IRS decreased significantly in subjects with the highest consumption of dairy products or grain, thus demonstrating an additive effect.
The three consecutive day food record method has some limitations, in particular the seasonal availability of some types of food. This was not the case for the food items analysed here, which are regularly available and eaten throughout the year in the three regions investigated. Further adjustment for season did not change the results significantly. Subjects under‐reporting a low energy intake may have biased the relation between food intake and IRS. When these subjects were not considered in the statistical analyses the results were not significantly altered.
In our population sample, the highest dairy product and grain consumption was associated with a more healthy profile, whereas such differences were not observed between subjects with the highest consumption of fish or with the lowest consumption. Thus the negative association between IRS and food components could be confounded by healthy profiles. After adjustment for healthy behaviours the inverse association between food intakes and IRS remained significant. Moreover, when the statistical analyses were done again after excluding subjects with high levels of physical activity, not only did the negative associations remain statistically significant but the strength of the relations tended to increase as well. Similar results were obtained when current smokers or subjects treated for hypertension or dyslipidaemia were excluded from the analyses.
Although statistical models had been adjusted for various environmental factors and potential confounders, with their corresponding records excluded from the analyses, the possibility of residual confounding by unmeasured factors cannot be entirely excluded. Moreover, the main limitation of our study is its observational design.
We observed an inverse relation between dairy product intake and IRS as mentioned in previous reports of observational studies.1,2,4
Our results showing a negative association between a diet rich in grain and the risk of IRS are less convincing than other reports.1,5
The negative association between fish and IRS is consistent with the results obtained in Alaska native population7
or in elderly people.6
However, the inverse association had not been reported in another French male population recruited from the social security system and not directly selected at random from the general population.1
Moreover, subjects had been selected from other geographical regions and the dietary methodology was different (food frequency questionnaire). However, inverse relations between IRS and dairy products or grain were similar.
What is already known on this subject
- Consumption of dairy products, grain, and fish has each been shown to be inversely associated with insulin resistance syndrome.
What this study adds
- Diet patterns characterised by a high consumption of dairy products, fish, or grain were associated with a lower probability of presenting with an insulin resistance syndrome.
- The combination of these food intakes tended to be more favourable than the consumption of each one separately and dramatically decreased the risk of having a metabolic syndrome.
Our study identified an eating pattern composed of a combination of high levels of fish, dairy products, and grain which was associated with very low frequency of IRS (13.1%) and a low risk of having the condition (odds ratio
0.21 (95% confidence interval, 0.10 to 0.44)). This risk was even lower when the consumption was high for only one component of the three types of food. Some epidemiological studies have examined the relation between food patterns and IRS using cluster or principal components analysis. Such multivariate techniques make comparisons with other studies difficult because distinct food clusters or food components identified are dependent on the population studied. However, it has been shown in a UK cohort study that component 1 of a principal component analysis—characterised by the frequent intake of salad vegetables, fruits, fish, pasta, and rice and a low intake of fried foods, sausages, fried fish, and potatoes—appeared to be protective from the metabolic syndrome.29
In another population, the multi‐ethnic Insulin Resistance Atherosclerosis Study cohort, the “dark bread pattern” (high fibre breads, rice, pasta, and vegetables) was associated with the best level of insulin sensitivity.30
Though fish and some carbohydrates were also found to be negatively associated with IRS, in the present study vegetable and fruit consumptions were not linked to IRS, as was reported in the Framingham Offspring Study with fibre from vegetable and fruit.5
The specific effect of fruit, vegetable, or fibre on IRS frequency could not be shown, probably because of the high level of consumption of these food components in our study population, whatever the other eating patterns. Conversely, meat consumption was positively associated with IRS in our study, as reported previously. The association remained significant after multivariate adjustment.
Three of the five components of the metabolic syndrome (blood pressure, triglycerides, and HDL cholesterol) seem to be the preferential target of the nutritional pattern characterised by a high intake of dairy products, grain, and fish.
Several studies have demonstrated a significant and negative relation between dairy product intake and blood pressure. About 70% of the calcium intake is supplied by dairy products in Western countries.3,31,32,33
It has been shown that dietary calcium, acting through a decrease in 1,25‐(OH)2
‐vitamin D production, reduces the stimulus of cell calcium influx and thus induces a hypotensive effect.34
Moreover, it has been suggested that an antihypertensive action could be exerted by milk bioactive proteins inhibiting angiotensin converting enzyme.35
In addition, calcium provided by food or in supplements causes a decrease in triglyceride levels36
and an increase in HDL cholesterol levels,37
though other studies have reported no such effect.
Diets including fish and with a 30% fat content reduce triglycerides and total and LDL cholesterol and increase HDL2 cholesterol.8
In patients with an increased risk of coronary heart disease, a high fish oil intake favourably affects VLDL and HDL cholesterol.38
In an elderly population, a low consumption of fish may protect against the development of impaired glucose tolerance and diabetes mellitus.6
A lower prevalence of impaired glucose tolerance and diabetes is associated with daily seal oil or salmon consumption in Alaskan natives.7
A role of carbohydrates with a high or low glycaemic index in insulin resistance has not been demonstrated clearly and the available data are controversial.39
Our study shows that patterns characterised by a high consumption of dairy products, fish, or grain are associated with a lower probability of presenting with an IRS. The combination of these food intakes tends to be more favourable than the consumption of each food type separately, and dramatically decreased the risk of having a metabolic syndrome.