The study, led by researcher Heather Vincent, was published in the Journal of Human Nutrition and Dietetics and aimed to determine whether the PI score is related to adiposity, weight gain, oxidative stress and inflammation.
Phytochemicals, bioactive compounds linked with chronic disease reduction, include substances such as allin from garlic, lycopene from tomatoes, isoflavones from soy, beta carotene from orange squashes and anythocyanins from red wine, among others.
‘Potential mechanisms of protection by a phytochemical rich diet includes the lowering of cardiovascular disease precursors, the lowering of oxidative stress and inflammation, and the preservation of vascular function as well as a lower incidence of obesity,’ said the authors.
The researchers explain that the premise of the PI measure is to divide the energy supplied by foods high in phytochemicals by the total energy consumed from all foods as a ratio score:
‘A vegan diet (excluding potato products, hard liquors and refined sugars) could have a score of 100, whereas less optimal dietary patterns, such as those in Western diets may range below 20,’ they added.
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 had to meet certain criteria prior to enrolment in the study such as no participation in regular physical activity, no chronic health problems or smoking, no history of cardiovascular, metabolic or respiratory disease, and no consumption of antioxidant supplements within the past six months.
They said that participants were broken into two groups: normal weight and overweight-obese, with three-day dietary records analysed for food items, food groups, energy and the PI score at repeated time points.
After a 12 hour fast blood plasma samples were collected from the cohort and analysed by colorimetric or an enzyme-linked immunoabsorbent assay for cholesterol subfractions, glycated haemoglobin, total antioxidant status, lipid hydroperoxides, cytokines (interleukins-1b and -6) and C-reactive protein), added the researchers.
According to the team, the trial results showed that PI scores for the normal weight and overweight groups were 23.5 and 13.2 respectively.
“Body mass, BMI, waist circumference, waist-to hip ratio, body fat percentage, fat and fat free mass values were significantly greater in the overweight/obese group,’ states the article.
The researchers said that 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.
The results showed that the overweight group also had higher levels of oxidative stress and inflammation than their normal-weight peers, said the study.
The authors concluded that the PI score was inversely related to several indices of adiposity, weight gain and oxidative stress but not inflammation, and that all of the participants would benefit from increased consumption of phytochemical rich foods.
"The PI index might be an ideal, simple assessment that could provide important feedback to encourage the intake of these protective foods,’ they added.
Source: Journal of Human Nutrition and Dietetics
Published online ahead of print DOI: 10.1111/k/1365-277X.2009.00987.x
Title: Relationship of the dietary phytochemical index to weight gain, oxidative stress and inflammation in overweight young adults
Authors: H. K. Vincent, C.M. Bourguignon and A. G. Taylor