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Colorful Plant Foods Reduce Obesity Risk
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The authors of a new study propose a new “phytochemical index” rating to rank diets for their capacity to help reduce obesity risk and weight-related health problems

The Dietary Guidelines for Americans recommend eating more fruits and vegetables than most do.

And the USDA’s “Five a Day” program is designed to get Americans to consume five servings of fruits and vegetables daily.

Now, fascinating new evidence associates diets high in fruits and vegetables (and low in processed, “empty calorie” foods) with healthy weight.

That wasn’t so surprising, but the findings held true even when total calorie intake by people of healthy weight was the same as that of overweight folks... as long as their diets were relatively high in fruits and vegetables.

If these startling findings are confirmed, they will add weight control as a motive to eat more fruits and vegetables and fewer refined and processed foods.

The scientific term “phytochemical” refers to beneficial compounds found exclusively in plants that possess the power to help prevent chronic diseases.

Among many others, examples include sulfurous allin (garlic), red-yellow carotenoids (carrots, squashes, greens, and tomatoes), isoflavones (soy, flaxseed), glucosinolates (broccoli, kale, and other cruciferous veggies), and flavonoids (grapes, berries, cocoa, tea, extra virgin olive oil, and red wine).

Now, a new study led by sports medicine researcher Heather Vincent, Ph.D. adds another likely benefit of diets rich in phytochemicals.

Based on her team’s findings, people would lose weight were they to plan their diets using a new rating system they call the Phytochemical Index… a concept introduced in a 2004 paper by nutritionist and researcher Mark F. McCarty (McCarty MF 2004).

The Floridians' proposed Phytochemical Index (PI) measures the number of calories consumed from phytochemical-rich foods versus the calories consumed from foods low in phytochemicals… such as white flour or refined vegetable oil.

Specifically, the PI number for any given diet is the ratio of the calories it provides from high-nutrient phytochemical-rich foods to overall daily calories consumed.

In other words, diets that derive higher proportions of their total calories from nutrient-dense plant foods yield higher PI numbers.

This ratio may be an effective way to help people recognize and reduce their risk for weight gain and the chronic diseases associated with obesity.

This could hold true even if the PI concept is only used a general educational principle rather than a diagnostic/predictive tool… which seems more likely than the prospect of doctors assessing patients’ personal diets in detail and translating the results into PI numbers.

What the study showed… and suggests

University of Florida researchers analyzed the dietary patterns of 54 young adults, including normal-weight and overweight-to-obese individuals (Vincent HK et al. 2009).

In order to reduce the chance that other, non-dietary factors were responsible for any differences in PI the researchers might detect, the participants had to meet certain criteria:
  • No participation in regular physical activity
  • No chronic health problems or smoking
  • No history of cardiovascular, metabolic or respiratory disease
  • No consumption of antioxidant supplements within the past six months.
The participants took diet surveys repeatedly over the course of the two month study.

The average PI scores of the normal-weight and overweight-to-obese individuals were 23.5 and 13.2, respectively.

That is, the average PI score of the diets reported by the normal-weight participants was twice as high as the average PI score reported by the overweight-to-obese participants.

Surprisingly, the two groups consumed roughly the same average number of calories daily.

Therefore, the team concluded the phytochemicals and trace minerals abundant in colorful plant foods may help the body maintain a normal weight: “The PI index might be an ideal, simple assessment that could provide important feedback to encourage the intake of these protective foods” (Vincent HK et al. 2009).

Overweight and obese individuals have physical and biochemical characteristics known to trigger the production of even more free radicals… these include excess abdominal fat and over-expression of certain enzymes, immune system proteins, and hormones.

Phytochemicals cut inflammation and retard cell aging

The overweight and obese participants also had higher levels of oxidative stress—from an excess of free radicals and lack of antioxidants—and chronic low-level inflammation, which promotes diabetes, cancer, and cardiovascular disease.

Excess free radicals from stress and pollution can overwhelm the body’s own antioxidant network and damage our cells… but plant-derived phytochemical antioxidants help combat free radicals and the inflammation they can induce.

As noted, the normal-weight/high-PI and overweight/lowPI participants reported similar calorie intakes.

However, foods high in phytochemicals are usually also high in fiber and low in fats and sugars, so they’re more filling and much less likely to yield blood sugar spikes and excess calorie intake.

As the authors of one review article put it, “Laboratory studies suggest that energy-dense foods and energy-dense diets have a lower satiating power and may result in passive overeating and therefore weight gain” (Drewnowski A, Darmon N 2005).

And the antioxidant properties of many phytochemicals are only one important reason for eating nutrient-rich plant-based foods.

For example, research suggests that a plant-based diet helps deter heart disease by improving many relevant risk factors.   And cruciferous veggies contain compounds with lab-demonstrated (but clinically untested) anti-cancer properties.

What is your diet’s PI number?
It’s pretty simple, really. Diets rich in colorful fruits and vegetables get high PI rankings, because some of the best phytochemicals also serve as bright pigments.

And diets that contain whole grains instead of refined flour would also score high on the PI scale, since they are rich in fiber and phytochemical antioxidant s.

As Vincent said, “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.”

She suggests, however, that we need not go to extremes to achieve a better PI.

Substituting just one or two low-scoring food choices a day with more phytochemical-rich alternatives can make a huge difference.

For example, rather than buttered white toast or bagel, start your day with some fresh fruit and yogurt on unsweetened whole grain cereal… or savor some smoked salmon on whole grain toast with a “schmeer” of avocado and a tomato slice.

“We always want to encourage people to go back to the whole sources of food, eating more of the non-processed foods if we can help it,” said Vincent. “That would be the bottom line for anyone, regardless of age and body size, keep going back to the purer plant-based foods. Remembering to eat the good quality food first.”

Amen, we say!

  • Drewnowski A, Darmon N. The economics of obesity: dietary energy density and energy cost. Am J Clin Nutr. 2005 Jul;82(1 Suppl):265S-273S. Review.
  • McCarty MF. Proposal for a dietary "phytochemical index". Med Hypotheses. 2004;63(5):813-7.
  • McCarty MF. The origins of western obesity: a role for animal protein? Med Hypotheses. 2000 Mar;54(3):488-94.
  • Newby P.K. Plant foods and plant-based diets: protective against childhood obesity? Am J Clin Nutr 2009 May, 89(5):1572S-1587S. Epub 2009 Mar 25.
  • Rao V, Al-Weshahy A. Plant-based diets and control of lipids and coronary heart disease risk. Curr Atheroscler Rep. 2008 Dec, 10 (6):478-85. [Pub Med]
  • Vincent HK, Bourguignon CM, Taylor AG. Relationship of the dietary phytochemical index to weight gain, oxidative stress and inflammation in overweight young adults. J Hum Nutr Diet. 2009 Sep 4. [Epub ahead of print]

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