A new study provides more evidence that supports eating a healthy diet low in meat and high in plant-based foods like fruits and vegetables, to tackle obesity and prevent disease.

According to research from the University of Florida, eating more plant-based foods such as leafy green vegetables before other foods, which are rich in substances called phytochemicals, could help people to battle metabolic processes that lead to obesity and heart disease. Scientists found that these foods seemed to prevent oxidative stress in the body, a process associated with obesity and the onset of disease.

To get enough of these protective phytochemicals, researchers suggest eating plant-based foods such as leafy greens, fruits, vegetables, nuts and legumes at the start of a meal. The study author explained:

"Fill your plate with colorful, low-calorie, varied-texture foods derived from plants first. By slowly eating phytochemical-rich foods such as salads with olive oil or fresh-cut fruits before the actual meal, you will likely reduce the overall portion size, fat content and energy intake. In this way, you're ensuring that you get the variety of protective, disease-fighting phytochemicals you need and controlling caloric intake."

The researchers studied a group of 54 young adults, analyzing their dietary patterns over a three-day period, repeating the same measurement eight weeks later. The participants were broken into two groups: normal weight and overweight-obese.

Although the adults in the two groups consumed about the same amount of calories, overweight-obese adults consumed fewer plant-based foods and subsequently fewer protective trace minerals and phytochemicals and more saturated fats. They also had higher levels of oxidative stress and inflammation than their normal-weight peers. These processes are related to the onset of obesity, heart disease, diabetes and joint disease, according to the author.

"Diets low in plant-based foods affect health over the course of a long period of time," "This is related to annual weight gain, low levels of inflammation and oxidative stress. Those are the onset processes of disease that debilitate people later in life."

Oxidative stress occurs when the body produces too many damaging free radicals and lacks enough antioxidants or phytochemicals to counteract them. Because of excess fat tissue and certain enzymes that are more active in overweight people, being obese can actually trigger the production of more free radicals, too.

Many phytochemicals have antioxidant properties, and can help to combat free radicals. Phytochemicals include substances such as allicin from garlic, lycopene from tomatoes, beta carotene from carrots and anythocyanins from blueberries, among others.

The study author said:

"People who are obese need more fruits, vegetables, legumes and wholesome unrefined grains,"

"In comparison to a normal-weight person, an obese person is always going to be behind the eight ball because there are so many adverse metabolic processes going on."

A starting point is to replace pre-packaged snacks and other processed foods which are high in sugar, artificial flavourings and low in nutrients, with phytochemical-rich foods such as fresh produce and other whole food from good quality plant-based sources.

Research paper details:

Vincent HK, Bourguignon CM, Taylor AG. Relationship of the dietary phytochemical index to weight gain, oxidative stress and inflammation in overweight young adults. Journal of Human nutrition and Dietetics, 2009.