Lower Levels of Dietary Fat Increase the Risk of Ischemic Stroke in Men
ABSTRACTS & COMMENTARY
Sources: Gillman MW, et al. JAMA 1997;278:2145-2150; Sherwin R, Price TR. Editorial. JAMA 1997;278:2185-2186.
Gillman et al examined the association of stroke incidence with intake of fat and type of fat among 832 men aged 45-65 years during 20 years of follow-up. Diet was assessed at baseline (1966-1969) by a single 24-hour dietary recall, from which intakes of calories and fat were estimated (see Table 1). Subjects were divided into quintiles according to total fat intake (see Table 2) and type of fat as a percentage of calories.
Ischemic strokes occurred in 61 subjects during the follow-up period. Risk of ischemic stroke declined across the increasing quintile of total fat (see Table 2; log-rank trend, P = 0.008), saturated fat (P = 0.002), and monounsaturated fat (P = 0.008) but not polyunsaturated fat (P = 0.33). Adjustment for cigarette smoking, glucose intolerance, body mass index, blood pressure, blood cholesterol level, physical activity, and intake of fruits, vegetables, and alcohol did not change the results.
Although fat intake predicts coronary artery disease (CAD) and the presence of CAD is a risk factor for stroke, these data suggest that fat intake does not increase stroke risk. In fact, fat intake was inversely associated with the incidence of ischemic stroke. Total polyunsaturated fat intake had little effect on stroke risk.
Sherwin and Price, in an editorial comment, suggest that the study be repeated in other populations, including women, and that further animal experiments are required to determine the mechanism by which higher levels of dietary fat appear to protect against ischemic stroke.
COMMENT BY JOHN J. CARONNA, MD
The finding that lower levels of dietary fat are associated with a higher risk of ischemic stroke has been reported previously in Asian1 and Asian American2 populations. The data of Gillman et al have attracted media attention because they contradict the view that total fat and saturated fat intake should be limited. Current National Dietary Guidelines recommend that total fat be limited to 30% of calories and saturated fat to 10%.3 The rationale behind these recommendations is that lower levels of dietary fat lead to both lower levels of blood cholesterol and a lower risk of obesity, two factors associated with CAD.
Intake of fat at baseline in 832 men
Type of Fat Grams * Percentage of total calories *
Saturated 44 ± 18 15 ± 4
Polyunsaturated 16 ± 8 5 ± 2
Monounsaturated 46 ± 18 16 ± 4
Total 114 ± 51 39 ± 9
* mean ± SD
The present data emphasize that extreme restriction of dietary fat intake may have potential risks and that a diet high in monounsaturated fats which do not increase cholesterol may be the most prudent diet to protect both heart and brain. (Dr. Caronna is Vice-Chairman, Department of Neurology, Cornell University Medical Center, and Professor of Clinical Neurology, New York Hospital.)
Baseline intake of total fat by quintiles and risk of ischemic stroke
Total fat intake as % Age-adjusted stroke cumulative Quintile of calories-mean (range) incidence rate per 1000
1 (n = 166) 26 (10-32) 112
2 (n = 166) 35 (32-37) 85
3 (n = 167) 40 (37-42) 57
4 (n = 167) 44 (42-47) 63
5 (n = 166) 51 (47-63) 41