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Dietary factors, ranging from fatty acids, vitamins and minerals to food groups, have been shown to be associated with the risk of developing CVD and type 2 diabetes. This evidence is summarised in

Table 1.1 and Table 1.2. There is convincing evidence that fruit and vegetables, fish and fish oils, unsaturated fatty acid, potassium and low to moderate alcohol consumption are protective against CVD, whereas trans fatty acids, saturated fatty acids and high sodium intake increase risk. A recent Cochrane review of 48 intervention trials reported the quality of dietary fat is more important for cardiovascular (CV) health than reducing total fat intake (20). In trials lasting at least 2 years, CV risk was reduced when saturated fat was replaced with unsaturated fat but not when total fat intake was reduced. It is not clear whether monounsaturated or polyunsaturated fat is more beneficial for CV health (20).

Table 1.1. Summary of the strength of evidence on dietary factors and risk of developing cardiovascular disease

Decreased risk No relationship Increased risk

Strong evidence

Vegetables and fruits (including berries)

Vitamin E supplements Myristic and palmitic acids

Trans fatty acids

Fish and fish oils (EHA and DHA) High sodium intake

Linoleic acid Potassium

Low to moderate alcohol intake (for coronary heart disease)

Moderate evidence

α-linolenic acid Stearic acid Dietary cholesterol

Oleic acid Unfiltered boiled coffee

Non starch polysaccharides Wholegrain cereals Nuts (unsalted) Plant sterols/stanols Folate

Weak evidence

Flavonoids Fats rich in lauric acid

Soy products Beta-carotene supplements

Insufficient evidence

Calcium Carbohydrates

Magnesium Iron

Vitamin C

Table modified from Diet, nutrition and the prevention of chronic diseases. World Health Organization,

Table 1.2. Summary of the strength of evidence on dietary factors and risk of developing type 2 diabetes

Decreased risk No relationship Increased risk

Moderate evidence

Non starch polysaccharides Saturated fats

Weak evidence

n-3 fatty acids Total fat

Low glycemic index foods Trans fatty acids

Insufficientevidence

Vitamin E Excessive alcohol

Chronium Magnesium Moderate alcohol

Table modified from Diet, nutrition and the prevention of chronic diseases. World Health Organization,

Food and Agriculture Organization. Geneva: World Health Organization; 2003 (21).

There is evidence dietary modification can reduce the risk of CVD and type 2 diabetes. A Cochrane review of 38 trials concluded that dietary advice was effective in making modest beneficial changes in CVD risk factors over approximately 10 months (22). Advice given to participants focused mainly on reducing fat and salt intake and increasing intake of fruit, vegetables and dietary fibre. Dietary advice reduced total and LDL cholesterol by 0.16mmol/L and 0.18mmol/L respectively in studies ranging in duration from 2-34 months. In studies ranging from 3 to 36 months, dietary advice reduced systolic blood pressure by 2.07mmHg and diastolic blood pressure by 1.15mmHg. Although none of the trials included in the review were of sufficient duration to determine if dietary

intervention could reduce CV events, it was estimated that dietary advice could reduce the incidence of coronary heart disease by 12% and stroke by 11%.

In addition to reducing the risk of CVD, lifestyle changes that include dietary modification have also been shown to reduce the risk of developing type 2 diabetes. Two large randomised controlled trials of individuals with impaired glucose tolerance reported dietary and lifestyle changes could reduce the incidence of diabetes compared to a control group. The Finnish Diabetes Prevention study (23) followed 522 overweight men and women with impaired glucose tolerance for an average of 3.2 years. During the trial the risk of developing type 2 diabetes was reduced by 58% in the intervention group. The Diabetes Prevention Program (24) compared the development of type 2 diabetes in participants with impaired glucose tolerance randomly assigned to standard lifestyle

recommendations plus placebo, standard lifestyle recommendations plus metformin (a drug used to treat high blood sugar) or an intensive lifestyle intervention. The average follow-up was 2.8 years. The incidence of diabetes was 58% lower in the intensive lifestyle intervention group and 31% lower

in the metformin group than the placebo group. The incidence of diabetes was 39% lower in the intensive lifestyle group than the metformin group. The benefits of lifestyle intervention or metformin in preventing or delaying the onset of diabetes was found to persist 10 years after

randomisation (25). The interventions used in these trials included a combination of diet and physical activity to promote weight loss and therefore it is impossible to separate the effect of dietary

changes alone.

However, a Cochrane review estimated diet alone could reduce the risk of developing diabetes by 33% over 6 years in individuals with impaired glucose tolerance (26). This estimate was based on only two studies that followed 358 participants. The Da Qing Study compared participants randomised to a diet only intervention (n=130) to those in a control group (n=133) (27). The diet only group was advised to consume 55-65% of total energy from carbohydrate, 10-15% of energy from protein and 25-30% of energy from fat. Participants were encouraged to consume more vegetables and control their intake of alcohol and simple sugars. Weight loss of 0.5-1.0 kg per month was advised for participants with a BMI above 25kg/m2, until a BMI of 23kg/m2 was achieved. The cumulative incidence of diabetes after 6 years was 68% in the control group and 44% in the diet group. Thus the diet intervention group had a significant reduction in the incidence of diabetes compared with the control group.

The Oslo Diet and Exercise Study compared participants randomised to a diet only intervention (n=52) with a control group (n=43). The dietary intervention recommended increased consumption of fish and fish products and energy restriction for those who were overweight or had high blood pressure (28). After 12 months of dietary intervention there were significant reductions in insulin resistance, fasting insulin, fasting proinsulin, fasting blood glucose, BMI, fasting triglycerides and significant increase in HDL cholesterol (29).