Here are half a dozen studies on diet (see below for all abstracts and links).  The first three are about the benefits of healthy lifestyle.  Trichopoulou & colleagues evaluated the contribution of nine widely accepted components of the Mediterranean diet (high intake of vegetables, fruits and nuts, legumes, fish, and cereals; low intake of meat and dairy; high ratio of monounsaturated to saturated lipids; and moderate intake of ethanol) in the inverse association of this diet with all cause mortality.  They concluded that "The dominant components of the Mediterranean diet score as a predictor of lower mortality are moderate consumption of ethanol, low consumption of meat and meat products, and high consumption of vegetables, fruits and nuts, olive oil, and legumes. Minimal contributions were found for cereals and dairy products, possibly because they are heterogeneous categories of foods with differential health effects, and for fish and seafood, the intake of which is low in this population."  Moderate alcohol consumption was defined as ethanol intake for men of >/=10 g/day and </=50 g/day, and women >/=5 g/day and </=25 g/day.  A unit of alcohol is equivalent to about 8 grams of ethanol.  Alcohol intake mostly involved wine drunk during meals.  The authors noted that " ... reports now suggest that even white wines contain antioxidant compounds and that wine may modulate the health effects of other nutritional compounds in the stomach."

Djousse et al looked at lifestyle and risk of heart failure in men (about 20% of 40 year olds will eventually develop heart failure).  They found that adhering to four or more of six healthy lifestyle behaviours halved the risk.  The six behaviours assessed at were "normal body weight, not smoking, regular exercise, moderate alcohol intake, consumption of breakfast cereals, and consumption of fruits and vegetables."  Meanwhile Forman & colleagues reported on lifestyle and risk of hypertension in women.  They examined the effects of a rather interesting set of six behaviours - "a body mass index (BMI) of less than 25, a daily mean of 30 minutes of vigorous exercise, a high score on the Dietary Approaches to Stop Hypertension (DASH) diet based on responses to a food frequency questionnaire, modest alcohol intake up to 10 g/d, use of nonnarcotic analgesics less than once per week, and intake of 400 {micro}g/d or more of supplemental folic acid."  Apparently "All 6 modifiable risk factors were independently associated with the risk of developing hypertension during follow-up."  Very few people indeed ticked all six boxes (0.3% of this population) - if they did, they had only a fifth the risk of developing high blood pressure over 14 years of follow-up.  The most important of the six factors for avoiding hypertension in this study was having a BMI of less than 25.  To calculate your BMI click here.

The next two studies I mention are slightly "disappointing" ones on the hoped for benefits of fish oils.  Devore et al followed up over 5,000 people, aged 55 or older, for about 10 years and found no reduction in dementia risk for those eating more fish.  Strom et al looked at rates of post-partum depression (PPD) in a large group of over 54,000 pregnant women.  They concluded: "Overall, our data from a large prospective cohort linked with high-quality registers showed little evidence to support an association between intake of fish or n-3 PUFAs and PPD."  It seems very likely that we should aim for an overall healthy diet rather than hope for too much from any one particular ingredient.  However in the last study I mention in this post, Banel & Hu reported on "Effects of walnut consumption on blood lipids and other cardiovascular risk factors: a meta-analysis and systematic review."  They wrote "When compared with control diets, diets supplemented with walnuts resulted in a significantly greater decrease in total cholesterol and in LDL-cholesterol concentrations ... significant benefits for certain antioxidant capacity and inflammatory markers and had no adverse effects on body weight ... Overall, high-walnut-enriched diets significantly decreased total and LDL cholesterol for the duration of the short-term trials. Larger and longer-term trials are needed to address the effects of walnut consumption on cardiovascular risk and body weight."

Trichopoulou, A., C. Bamia, et al. (2009). "Anatomy of health effects of Mediterranean diet: Greek EPIC prospective cohort study." BMJ 338(jun23_2): b2337-.  [Free Full Text]
 Objective To investigate the relative importance of the individual components of the Mediterranean diet in generating the inverse association of increased adherence to this diet and overall mortality. Design Prospective cohort study. Setting Greek segment of the European Prospective Investigation into Cancer and nutrition (EPIC). Participants 23 349 men and women, not previously diagnosed with cancer, coronary heart disease, or diabetes, with documented survival status until June 2008 and complete information on nutritional variables and important covariates at enrolment. Main outcome measure All cause mortality. Results After a mean follow-up of 8.5 years, 652 deaths from any cause had occurred among 12 694 participants with Mediterranean diet scores 0-4 and 423 among 10 655 participants with scores of 5 or more. Controlling for potential confounders, higher adherence to a Mediterranean diet was associated with a statistically significant reduction in total mortality (adjusted mortality ratio per two unit increase in score 0.864, 95% confidence interval 0.802 to 0.932). The contributions of the individual components of the Mediterranean diet to this association were moderate ethanol consumption 23.5%, low consumption of meat and meat products 16.6%, high vegetable consumption 16.2%, high fruit and nut consumption 11.2%, high monounsaturated to saturated lipid ratio 10.6%, and high legume consumption 9.7%. The contributions of high cereal consumption and low dairy consumption were minimal, whereas high fish and seafood consumption was associated with a non-significant increase in mortality ratio. Conclusion The dominant components of the Mediterranean diet score as a predictor of lower mortality are moderate consumption of ethanol, low consumption of meat and meat products, and high consumption of vegetables, fruits and nuts, olive oil, and legumes. Minimal contributions were found for cereals and dairy products, possibly because they are heterogeneous categories of foods with differential health effects, and for fish and seafood, the intake of which is low in this population.

Djousse, L., J. A. Driver, et al. (2009). "Relation Between Modifiable Lifestyle Factors and Lifetime Risk of Heart Failure." JAMA 302(4): 394-400.  [Abstract/Full Text]
 Context The lifetime risk of heart failure at age 40 years is approximately 1 in 5 in the general population; however, little is known about the association between modifiable lifestyle factors and the remaining lifetime risk of heart failure. Objective To examine the association between modifiable lifestyle factors and the lifetime risk of heart failure in a large cohort of men. Design, Setting, and Participants Prospective cohort study using data from 20 900 men (mean age at baseline, 53.6 years) from the Physicians' Health Study I (1982-2008) who were apparently healthy at baseline. Six modifiable lifestyle factors were assessed: body weight, smoking, exercise, alcohol intake, consumption of breakfast cereals, and consumption of fruits and vegetables. Main Outcome Measure Lifetime risk of heart failure. Results During a mean follow-up of 22.4 years, 1200 men developed heart failure. Overall, the lifetime risk of heart failure was 13.8% (95% confidence interval [CI], 12.9%-14.7%) at age 40 years. Lifetime risk remained constant in men who survived free of heart failure through age 70 years and reached 10.6% (95% CI, 9.4%-11.7%) at age 80 years. Lifetime risk of heart failure was higher in men with hypertension than in those without hypertension. Healthy lifestyle habits (normal body weight, not smoking, regular exercise, moderate alcohol intake, consumption of breakfast cereals, and consumption of fruits and vegetables) were individually and jointly associated with a lower lifetime risk of heart failure, with the highest risk in men adhering to none of the 6 lifestyle factors (21.2%; 95% CI, 16.8%-25.6%) and the lowest risk in men adhering to 4 or more desirable factors (10.1%; 95% CI, 7.9%-12.3%). Conclusion In this cohort of apparently healthy men, adherence to healthy lifestyle factors is associated with a lower lifetime risk of heart failure.

Forman, J. P., M. J. Stampfer, et al. (2009). "Diet and Lifestyle Risk Factors Associated With Incident Hypertension in Women." JAMA 302(4): 401-411.  [Abstract/Full Text]
 Context Hypertension is an important preventable risk factor for death among women. While several modifiable risk factors have been identified, their combined risk and distribution in the population have not been assessed. Objective To estimate the hypothetical fraction of hypertension incidence associated with dietary and lifestyle factors in women. Design, Setting, and Participants Prospective cohort study of 83 882 adult women aged 27 to 44 years in the second Nurses' Health Study who did not have hypertension, cardiovascular disease, diabetes, or cancer in 1991, and who had normal reported blood pressure (defined as systolic blood pressure of < or = 120 mm Hg and diastolic blood pressure of < or = 80 mm Hg), with follow-up for incident hypertension for 14 years through 2005. Six modifiable lifestyle and dietary factors for hypertension were identified. The 6 low-risk factors for hypertension were a body mass index (BMI) of less than 25, a daily mean of 30 minutes of vigorous exercise, a high score on the Dietary Approaches to Stop Hypertension (DASH) diet based on responses to a food frequency questionnaire, modest alcohol intake up to 10 g/d, use of nonnarcotic analgesics less than once per week, and intake of 400 {micro}g/d or more of supplemental folic acid. The association between combinations of 3 (normal BMI, daily vigorous exercise, and DASH-style diet), 4 (3 low-risk factors plus modest alcohol intake), 5 (4 low-risk factors plus avoidance of nonnarcotic analgesics), and 6 (folic acid supplementation > or = 400 {micro}g/d) low-risk factors and the risk of developing hypertension was analyzed. Main Outcome Measures Adjusted hazard ratios for incident self-reported hypertension and population attributable risks (PARs). Results A total of 12 319 incident cases of hypertension were reported. All 6 modifiable risk factors were independently associated with the risk of developing hypertension during follow-up after also adjusting for age, race, family history of hypertension, smoking status, and use of oral contraceptives. For women who had all 6 low-risk factors (0.3% of the population), the hazard ratio for incident hypertension was 0.22 (95% confidence interval [CI], 0.10-0.51); the hypothetical PAR was 78% (95% CI, 49%-90%) for women who lacked these low-risk factors. The corresponding hypothetical absolute incidence rate difference (ARD) was 8.37 cases per 1000 person-years. The PARs were 72% (95% CI, 57%-82%; ARD, 7.76 cases per 1000 person-years) for 5 low-risk factors (0.8% of the population), 58% (95% CI, 46%-67%; ARD, 6.28 cases per 1000 person-years) for 4 low-risk factors (1.6% of the population), and 53% (95% CI, 45%-60%; ARD, 6.02 cases per 1000 person-years) for 3 low-risk factors (3.1% of the population). Body mass index alone was the most powerful predictor of hypertension, with a BMI of 25 or greater having an adjusted PAR of 40% (95% CI, 38%-41%) compared with a BMI of less than 25. Conclusions Adherence to low-risk dietary and lifestyle factors was associated with a significantly lower incidence of self-reported hypertension. Adopting low-risk dietary and lifestyle factors has the potential to prevent a large proportion of new-onset hypertension occurring among young women.

Devore, E. E., F. Grodstein, et al. (2009). "Dietary intake of fish and omega-3 fatty acids in relation to long-term dementia risk." Am J Clin Nutr 90(1): 170-176.  [Abstract/Full Text] 
Background: Greater fish and omega-3 (n-3) polyunsaturated fatty acid (PUFA) intake may reduce dementia risk; however, previous studies have reported conflicting results, which were largely based on short-term follow-up. Objective: The objective was to study the dietary consumption of fish and omega-3 PUFAs in relation to long-term dementia risk. Design: We studied 5395 participants aged > or = 55 y in the Rotterdam Study who were free of dementia and reported dietary information at baseline. We used age- and sex-adjusted Cox proportional hazard and multivariate-adjusted models to evaluate the relative risk of dementia and Alzheimer disease (AD) across categories of typical fish intake (none, low, and high) and fish type consumed (none, lean, and fatty). We also evaluated dementia and AD risk across tertiles of omega-3 PUFA intake, specifically, total long-chain omega-3 fatty acids: eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA),{alpha} -linolenic acid, and EPA and DHA individually. Results: During an average follow-up of 9.6 y, dementia developed in 465 participants (365 with a diagnosis of AD). In multivariate-adjusted models, total fish intake was unrelated to dementia risk (P for trend = 0.7). Compared with participants who typically ate no fish, those with a high fish intake had a similar dementia risk (hazard ratio: 0.95; 95% CI: 0.76, 1.19), as did those who typically ate fatty fish (hazard ratio: 0.98; 95% CI: 0.77, 1.24). Dietary intakes of omega-3 PUFAs were also not associated with dementia risk, and the results were similar when we considered AD specifically. Conclusion: In this Dutch cohort, who had a moderate consumption of fish and omega-3 PUFAs, these dietary factors do not appear to be associated with long-term dementia risk.

Strom, M., E. L. Mortensen, et al. (2009). "Fish and long-chain n-3 polyunsaturated fatty acid intakes during pregnancy and risk of postpartum depression: a prospective study based on a large national birth cohort." Am J Clin Nutr 90(1): 149-155.  [Abstract/Full Text] 
Background: Mothers may be reluctant to receive medical treatment of postpartum depression (PPD), despite the detrimental consequences the disorder can impose on mother and child. Research on alternative methods of prevention and treatment of PPD is warranted. Previous studies have suggested that long-chain n-3 polyunsaturated fatty acids (PUFAs) might have a beneficial effect on depression. Objective: The objective was to explore the association between intake of fish and n-3 PUFAs during pregnancy and PPD in the Danish National Birth Cohort (DNBC). Design: Exposure information from the DNBC was linked to the Danish patient and prescription registries for data on clinically identified cases of depression up to 1 y postpartum. Intake of fish and n-3 PUFAs was assessed in midpregnancy with a food-frequency questionnaire. Admission to the hospital for PPD (PPD-admission) and prescription of antidepressants (PPD-prescription) were treated as separate outcomes. A total of 54,202 women were included in the present study sample. Results: Rates of depression were 0.3% (PPD-admission) and 1.6% (PPD-prescription). No association was observed between fish intake and risk of PPD-admission [crude odds ratio of 1.01 (95% CI: 0.52, 1.97) and adjusted odds ratio of 0.82 (95% CI: 0.42, 1.64)], whereas a higher risk of PPD-prescription was found for the lowest compared with the highest fish intake group [crude odds ratio of 1.61 (95% CI: 1.26, 2.06) and adjusted odds ratio of 1.46 (95% CI: 1.12, 1.90)]. No association was observed with respect to n-3 PUFA intake. Conclusion: Overall, our data from a large prospective cohort linked with high-quality registers showed little evidence to support an association between intake of fish or n-3 PUFAs and PPD.

Banel, D. K. and F. B. Hu (2009). "Effects of walnut consumption on blood lipids and other cardiovascular risk factors: a meta-analysis and systematic review." Am J Clin Nutr 90(1): 56-63.  [Abstract/Full Text]
Background: Consumption of nuts has been associated with a decreased risk of cardiovascular disease events and death. Walnuts in particular have a unique profile: they are rich in polyunsaturated fatty acids, which may improve blood lipids and other cardiovascular disease risk factors. Objectives: We aimed to conduct a literature review and a meta-analysis to combine the results from several trials and to estimate the effect of walnuts on blood lipids. Design: Literature databases were searched for published trials that compared a specifically walnut-enhanced diet with a control diet. We conducted a random-effects meta-analysis of weighted mean differences (WMDs) of lipid outcomes. Results: Thirteen studies representing 365 participants were included in the analysis. Diets lasted 4-24 wk with walnuts providing 10-24% of total calories. When compared with control diets, diets supplemented with walnuts resulted in a significantly greater decrease in total cholesterol and in LDL-cholesterol concentrations (total cholesterol: WMD = -10.3 mg/dL, P < 0.001; LDL cholesterol: WMD = -9.2 mg/dL, P < 0.001). HDL cholesterol and triglycerides were not significantly affected by walnut diets more than with control diets (HDL cholesterol: WMD = -0.2, P = 0.8; triglycerides: WMD = -3.9, P = 0.3). Other results reported in the trials indicated that walnuts provided significant benefits for certain antioxidant capacity and inflammatory markers and had no adverse effects on body weight [body mass index (kg/m2): WMD = -0.4, P = 0.5; weight (kg): WMD = -0.05, P = 0.97]. Conclusions: Overall, high-walnut-enriched diets significantly decreased total and LDL cholesterol for the duration of the short-term trials. Larger and longer-term trials are needed to address the effects of walnut consumption on cardiovascular risk and body weight.