The researchers from the University of Minnesota, say these two factors increase the risk of suffering from a cluster of risk factors known as metabolic syndrome by 25%.

Metabolic syndrome is a cluster of cardiovascular disease and diabetes risk factors and is characterised by excessive fat around the waist, high cholesterol, high blood sugar and high blood pressure.

The presence of three or more of the factors increases a person's risk of developing diabetes and cardiovascular disease.

Dr. Lyn Steffen, an associate professor of epidemiology at the University says finding that diet soda also promoted risk was initially a surprise but they suspect it may be associated with compensating for eating higher calorie food.

The researchers say the combination of lots of meat, fried foods and diet soda add up to heart disease and their conclusions add support to a growing body of evidence which has linked fast food with unhealthy lifestyles.

For the study the research team examined the diets of 9,514 people aged 45 to 64, and looked closely at what people were eating.

On the basis of a 66-item food frequency questionnaire, the participants were categorized into two groups: those with a "western-pattern" diet, heavy on processed meat, fried foods, red meat; and a "prudent-pattern" diet with more fruit and vegetables, with small amounts of fish and poultry.

The researchers found nine years later, even after smoking and exercise were factored in, that 3,782, nearly 40%, developed three or more of the factors linked to metabolic syndrome.

Dr. Steffen says it is not just meat that adds inches to the waist, increases blood pressure and lowers HDL, it is fried foods as well, while dairy products, by contrast, appeared to offer some protection against metabolic syndrome.

Dr. Steffen says the study's results are clear - too much meat, fried foods and diet soda, do not add up to a healthy life and supports the link between fast-food consumption and an increase in metabolic risk factors.

According to health experts a healthy lifestyle encourages people to limit saturated fat, trans fat, cholesterol and sodium in their diet, cut down on sugars, eat plenty of vegetables, fruits and whole-grain foods, choose fat-free and low-fat dairy products and eat fish at least twice per week.

They also say physical activity and weight control are important and exposure to tobacco products should be avoided in order to achieve and maintain healthy cholesterol, blood pressure and blood glucose levels.

The study was funded by the National Heart, Lung, and Blood Institute and is published in the journal Circulation.