The puzzle of dietary fat intake and risk of ischemic stroke: a brief review of epidemiologic data

While coronary heart disease (CHD) and ischemic stroke share some major risk factors, limited epidemiologic data on dietary fats and vascular disease risk indicate that ischemic stroke is affected differently by these fatty acids than is CHD. The established associations between types of fat and CHD do not appear to apply to ischemic stroke. One explanatory hypothesis for the paradoxical observations is that arteriosclerosis in different types of cerebral arteries has different causal patterns. Fatty acids or blood lipids might not be as important as other factors, such as blood pressure, in the pathogenesis of a certain type of ischemic stroke. However, confirmatory data on the associations of fatty acids and subtype of ischemic stroke, including lacunar, atherosclerotic, and cardioembolic infarction, are lacking. The purpose of this review is to summarize the epidemiologic data on dietary fat and fatty acids in relation to ischemic stroke. Future investigations are needed to examine the effects of fatty acids on subtype of ischemic stroke and to clarify the possible differences of dietary fat in relation to ischemic stroke and CHD.     

Food sources, dietary behavior, and the saturated fat intake of Latino children.

BACKGROUND. Recent recommendations for Americans aged 2 and older call for a reduction in the average saturated fat intake to less than 10% of calories. METHODS. Using 24-hour dietary recalls collected from mothers of 4- to 7-year-old urban Latino children, we identified foods and dietary behavior patterns that distinguish children with higher and lower mean daily percentages of calories from saturated fat. RESULTS. Compared with children in the lowest quintile of intake, children in the highest quintile consumed more than twice as much saturated fat per day from high-fat milk products (18.5 g vs 7.8 g), mostly from whole milk. They did not consume different kinds of milk or different amounts of milk per eating occasion, but on average they consumed milk more frequently (2.8 vs 1.6 eating occasions per day). Even children in the lowest quintile, on average, exceeded the 10% of calories from saturated fat currently recommended. If low-fat (1% fat) milk had been substituted without other dietary changes, all but the highest two quintiles would have been within the recommended level. CONCLUSIONS. The substitution of low-fat for whole milk appears to be a key strategy for preschool children for achieving recommended levels of saturated fat intake.     

Medicaid data as a resource for epidemiologic studies: strengths and limitations

Large claims databases from third-party insurance programs such as Medicaid have attracted the interest of epidemiologists because of their enormous size and apparent comprehensiveness. Over 20 million people are covered by the various state Medicaid programs and most states maintain detailed computerized records of all reimbursed health care encounters on a recipient-specific basis. For states covering medication costs, data on drug exposures are particularly complete and accurate. However, Medicaid claims data also have many limitations that can pose major methodological difficulties. Foremost among these is the uneven validity and completeness of the diagnoses appearing on claims. Likewise, the unique identification of specific program participants is not straightforward, although useful approaches can often be developed to track individuals over time. Consideration of the limitations as well as the possible strengths of claims-based data makes it possible to choose appropriate study hypotheses as well as to attempt solutions, where possible, to the biases of this methodology.     

Newborn screening archives as a specimen source for epidemiologic studies: feasibility and potential for bias

PURPOSE: To evaluate the feasibility of obtaining dried blood spots (DBS) from newborn screening archives for subjects in epidemiologic studies and using these specimens for genotyping, and to evaluate the potential for bias in their use. METHODS: We attempted to locate DBS at Washington State's archives for 230 participants in a previous case-control study of childhood cancer, who were born 1978-1990. We compared characteristics of children for whom we did and did not locate specimens and attempted genetic polymorphism analyses (11 polymorphisms, 82-480 bp amplicons). RESULTS: We retrieved specimens for 203 (88%) children, including 199 (94%) born in months when a DBS catalog was available. Among the latter, the proportion with specimens located varied by birth place (e.g., hospital, home), maternal education, and prenatal smoking, but did not vary significantly by race/ethnicity. All genotyping assays were completed for all specimens, and among controls genotype distributions were in Hardy-Weinberg equilibrium and similar to previous reports. CONCLUSIONS: Newborn screening archives have potential to provide specimens for epidemiologic studies conducting genotyping and perhaps other assays, but the possibility that reliance on these resources could bias risk estimates must be considered.     

Impact of dietary fat content and fat oxidation on energy intake in humans

Three studies were performed to assess the effects of a high-fat diet and exercise-induced changes in fat oxidation on energy intake in humans. In the first study the short-term effect of a high-fat diet on spontaneous energy intake was investigated. The second study evaluated the long-term effect of a high-fat diet on adiposity and the third study evaluated the effect of exercise-induced changes in fat oxidation on short-term regulation of energy intake when subjects were consuming a high-fat diet. The results of these studies indicate that a high-fat diet induces a short-term hyperphagia, a high percentage of lipids in the usual diet is associated with a higher adiposity, and exercise may attenuate or amplify the high-fat, diet-induced hyperphagia, depending on the magnitude of the exercise-induced increase in fat oxidation.     

Developing a scoring method for evaluating dietary methodology in reviews of epidemiologic studies

We examined the quality of dietary assessment used by studies of prostate cancer and dietary fat in an attempt to explain the heterogeneity of their relative risk (RR) estimates. We reviewed the dietary assessment of 39 studies published in English that reported RRs for the association between prostate cancer and dietary fat intake derived from food frequency questionnaires (FFQs). We scored studies based on several objective measures of quality dietary assessment. Studies received no points for characteristics with unclear information. Studies scored 2 points for interviewer-completed FFQs, along with 2 points for quantitative assessments. They were scored 4 points for FFQs with more than 150 items, with an additional point for pretesting and 2 points for validated FFQs. Studies were given 1 point for describing each of the following characteristics: specifying the nutrient database used to convert foods to grams of fat, specifying quality control, attempting to measure dietary intake prior to diagnosis (recalled dietary period), and reporting the time needed to complete the FFQ. We then ranked studies based on their overall score: "high" for a score of 7 or greater out of 15 and "low" for lower scores. Two of the 39 studies that used quantitative methods other than a FFQ were excluded. Of the remaining 37 studies reviewed that used FFQs, only 16 were judged to have a high quality assessment of dietary fat. This review highlights the inconsistency of FFQ used in epidemiologic studies of dietary fat. Such variations in dietary measurement may be reflected in the variation in the magnitude of RRs reported for prostate cancer and dietary fat. The problems identified here include insufficient reporting of the details of dietary assessment, in addition to use of questionnaires with only a few food items to estimate a subject's dietary fat intake. It is imperative that journals include experts in the field of nutrition as reviewers of epidemiologic papers describing diet.     

Influences on intention to reduce dietary intake of fat and sugar

A theoretical understanding of factors influencing nutrition behavior can potentially enhance the effectiveness of educational strategy design. This cross-sectional study used the Ajzen and Fishbein theory of reasoned action to examine specific factors influencing intentions to reduce dietary intake of fat and sugar (“dieting”). A questionnaire was developed to measure belief, value and social influences on intention to reduce fat and sugar intake; the behavioral intention (BI) to reduce fat and sugar intake; and current self-reported fat and sugar restriction. The subjects were university health and non-health majors. Regression analysis revealed that both subjective norms and attitudes toward the behavior predicted the subject's intention to reduce fat and sugar intake. For health majors, the attitude toward the behavior was more influential in predicting BI; for the non-health majors, the subjective norm was more important. Those reporting current restriction of fat and sugar intake also had significantly more positive behavioral beliefs about health benefits than those not reporting restriction. Implications for the development of educational programs include the importance of identifying primary motivational factors (attitudes or social influences), and specific belief and value perceptions for intervention in targeted populations.     

Moderate dietary fat consumption as a risk factor for ischemic heart disease in a population with a low fat intake: a case-control study in Korean men

BACKGROUND: Dietary fat intake is associated with the incidence of ischemic heart disease (IHD) in Western countries. In populations in which both the average dietary fat consumption and the incidence of IHD are lower than in Western countries, the association of dietary fat intake with IHD incidence remains unknown. OBJECTIVE: We conducted a case-control study to examine the association of dietary fat with IHD incidence in Korean men. DESIGN: The case group consisted of 108 patients with electrocardiogram-confirmed myocardial infarction or angiographically confirmed (> or =50% stenosis) IHD who were admitted to a university teaching hospital in Seoul, Republic of Korea. The controls were 142 age-matched patients admitted to the departments of ophthalmology and orthopedic surgery at the same hospital. Dietary fat intake was assessed by a nutritionist using a semiquantitative food-frequency questionnaire. Body mass index (BMI), cigarette use, alcohol intake, exercise, and history of disease were determined during an interview and examination. RESULTS: In a univariate analysis, the mean percentages of energy from total fat, saturated fatty acids, and monounsaturated fatty acids were significantly higher in the cases than in the controls. BMI, smoking, and a history of hypertension were associated with the occurrence of IHD. In multiple logistic analyses, total fat intake was a significant risk factor (odds ratio: 1.08 for 1% of energy intake; 95% CI: 1.02, 1.14) after adjustment for BMI and smoking. CONCLUSION: In a population with a relatively low fat intake (19% of energy intake), a moderate increase in total fat intake may be a risk factor for IHD.     

Differential recall as a source of bias in epidemiologic research

Differential recall between compared groups is discussed most often in the context of case-control studies. Cases, compared to controls, are suspected of providing a more complete report of their true exposure to an hypothesized risk factor, thereby biasing upwards the estimate of its effect. The present paper describes how differential recall can arise with any observational design in epidemiology; with any class of study variable, not only exposures; and may inflate or deflate the true value of the estimate of effect size. We list a variety of study designs and questionnaire tactics that aim to remedy these problems. The scope and magnitude of the bias created by differential recall and the efficacy of proposed remedies require further study.     

The intake of dietary indigestible fraction in the Spanish diet shows the limitations of dietary fibre data for nutritional studies

OBJECTIVE: To compare the intakes of dietary fibre (DF) and dietary indigestible fraction (DIF) in the Spanish diet and also to show the limitations of DF values for nutritional and epidemiological studies. DESIGN: This includes the following: (i) estimation of plant foods consumption in Spanish diet from national food consumption data obtained from annual surveys (6000 households, 700 hotels and restaurants and 200 institutions); (ii) determination of DIF content in plant foods using analytical methods that mimic physiological conditions; (iii) estimation of daily intakes of DIF and DF in the Spanish diet. RESULTS: DIF intake in the Spanish population was estimated at 41.5 g/person/day. DF intake (18.3 g/person/day) was considerably lower than the amount of carbohydrate necessary to maintain the daily bacterial cell turnover in large intestine ('carbohydrate gap'). The differences between DIF and DF values are a consequence of conceptual and methodological aspects. DIF, as the part of foods reaching the colon, comprises not only DF but also other indigestible compounds such as a fraction of resistant starch, protein, polyphenols and other associated compounds. Analytical conditions are closer to actual physiological conditions in the determination of DIF than in DF analysis. CONCLUSIONS: DF intake underestimates a major part of the dietary substrates that enter the colon. DIF intake more closely matches the amount of substrates needed to maintain a typical human colonic microflora. DIF may be a good alternative to DF for nutritional and epidemiological studies.     

Influence of dietary conjugated linoleic Acid and fat source on body fat and apoptosis in mice

OBJECTIVE: To determine whether altered dietary essential fatty acid (linoleic and arachidonic acid) concentrations alter sensitivity to conjugated linoleic acid (CLA)-induced body fat loss or DNA fragmentation. RESEARCH METHODS AND PROCEDURES: Mice were fed diets containing soy oil (control), coconut oil [essential fatty acid deficient (EFAD)], or fish oil (FO) for 42 days, and then diets were supplemented with a mixture of CLA isomers (0.5% of the diet) for 14 days. Body fat index, fat pad and liver weights, DNA fragmentation in adipose tissue, and fatty acid profiles of adipose tissue were determined. RESULTS: The EFAD diet decreased (p < 0.05) linoleic and arachidonic acid in mouse adipose tissue but did not affect body fat. Dietary CLA caused a reduction (p < 0.05) in body fat. Mice fed the EFAD diet and then supplemented with CLA exhibited a greater reduction (p < 0.001) in body fat (20.21% vs. 6.94% in EFAD and EFAD + CLA-fed mice, respectively) compared with mice fed soy oil. Dietary FO decreased linoleic acid and increased arachidonic acid in mouse adipose tissue. Mice fed FO or CLA were leaner (p < 0.05) than control mice. FO + CLA-fed mice did not differ in body fat compared with FO-fed mice. Adipose tissue apoptosis was increased (p < 0.001) in CLA-supplemented mice and was not affected by fat source. DISCUSSION: Reductions in linoleic acid concentration made mice more sensitive to CLA-induced body fat loss only when arachidonic acid concentrations were also reduced. Dietary essential fatty acids did not affect CLA-induced DNA fragmentation.