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The Phytochemical Diet

September 15, 2009 Written by JP       [Font too small?]

Many doctors and nutritionists have long held the view that eating more fruits and vegetables is key to maintaining a healthy weight. Sometimes there’s some disagreement about what kinds of plant foods best serve this purpose. But ultimately, there is a general consensus that this is a positive step we can take towards combating obesity. It’s been widely assumed that fruits and veggies largely replace less nutritious foods in the average diet. This is frequently the case. However, recent scientific developments help explain exactly why plant-based foods have a fat fighting effect. This additional knowledge may provide a renewed incentive for eating more natural, whole foods.

The power of fruits and vegetables goes far beyond dietary fiber, minerals and vitamins. Every piece of produce that you see at your local grocery store or that grows in your garden is literally packed with substances known as “phytochemicals”. These are chemicals that are known to protect the human body. They very often possess potent antioxidant properties and are being investigated for their potential roles in addressing a broad array of health conditions. (1,2,3,4,5)

The importance of phytochemicals is so great that scientists are attempting to grow crops that contain higher levels of them. They’re doing this by selectively breeding the most potent members of various vegetable families in specific climates and environmental conditions. There are two primary reasons for doing so: 1) Scientists believe that it’s advantageous to have an optimal intake of these substances on a regular basis; and 2) They’d like those who don’t eat much produce to get more significant amounts of phytochemicals when they do. (6)

A just published study in the Journal of Human Nutrition and Dietetics points to a new connection between plant food consumption and weight. A group of 54 “normal weight” and overweight participants (aged 18 – 30) kept a food diary for three days. The researchers analyzed the food questionnaires and focused on several categories such as caloric intake (energy), food groups and something called a “phytochemical index” (PI). A PI is defined as the “ratio of the energy from high nutrient, phytochemical-rich foods to overall daily energy consumed”. There were several key findings.

  • A lower intake of phytochemicals was found in the overweight and obese participants.
  • A poor PI was correlated to a higher body mass index, oxidative stress, waist circumference and waist-to-hip ratio.

The authors of this preliminary study concluded that, “The PI is inversely related to adiposity and oxidative stress in healthy young adult, and is responsive to body weight changes”. (7)

I used that first study as a springboard to try to determine why a higher intake of phytochemicals may help promote a healthier weight. Here’s some of what I discovered:

  • Blood Sugar - Eating and/or supplementing with phytochemicals tends to lower blood glucose and excessive insulin production. In particular, they may help moderate our post meal blood sugar response. Stable blood glucose supports healthy body weight and discourages the accumulation of abdominal obesity and the cardiovascular health risks that accompany it. (8,9,10)
  • Effects on Fat Cells - Certain phytochemicals might directly impact the life cycle of fat cells (adipocytes). It appears that they may decrease the volume of fatty tissue by: a) stimulating the breakdown of fat within adipocytes; b) inducing their death (apoptosis); and c) suppressing the growth of new fat cells (adipogenesis). (11,12)
  • Inflammation - It’s pretty well established that various phytochemicals can help temper chronic inflammation. Overweight individuals often exhibit higher levels of inflammatory markers, such as CRP (C-reactive protein). Many scientists believe that this very inflammation may contribute to weight gain and the many health issues that are affiliated with it. A diet rich in low-glycemic fruits and vegetables has been demonstrated to lower inflammatory compounds in the body. (13,14,15,16,17,18)
  • Probiotics - A recent experiment showed that the inclusion of blueberries in a test diet helped to reduce intestinal inflammation and supported the growth of beneficial bacteria. In a column I wrote last week, I described how pomegranate extracts could selectively discourage the growth of harmful microorganisms while, at the same time, supporting the growth of healthy bacteria (probiotics) in the digestive system. It’s been proposed that an imbalance of intestinal bacteria may contribute to obesity by promoting inflammation and insulin resistance. Perhaps this is why a study from July 2009 discovered that probiotic supplementation helped gastric bypass patients lose a considerable amount more weight than similar patients who did not receive the beneficial bacteria. (19,20,21)

CRP Levels According to Ethnicity, NHANES 1999–2004

Obesity Class (body mass index, kg/m2)
Mean CRP Level (mg/dl)
Non-Hispanic White Non-Hispanic Black Mexican American Other
Normal (<25.0) 0.11 0.12 0.15 0.13
Overweight (25.0–29.9) 0.24 0.24 0.31 0.20
Obesity Class 1 (30.0–34.9) 0.41 0.54 0.38 0.30
Obesity Class II (35.0–39.9) 0.63 0.42 0.41 0.66
Obesity Class III (≥40.0) 0.89 0.69 0.78 0.71
Source: J Gastrointest Surg. 2009 July; 13(7): 1205–1212 (link)

In May 2009, a paper was presented in the American Journal of Clinical Nutrition that tested the hypothesis that increased fruit and vegetable consumption could help manage weight in a high risk group – individuals who had recently stopped smoking. Over 89,000 European men and women participated in this evaluation which followed them for an average of 6.5 years. The authors concluded that, “Fruit and vegetable intake relates significantly, albeit weakly, to weight change. For persons who stop smoking, high fruit and vegetable intakes may be recommended to reduce the risk of weight gain”. (22)

Knowing what I know now, I wonder if a new study such be undertaken. If I were designing such a trial, I’d ask the participants to eat fruits and vegetables that are the richest in phytochemicals. For instance, I’d suggest eating spinach instead of iceberg lettuce or blueberries rather than white grapes. Another important piece of the puzzle may be to focus on phytochemical-rich whole fruits and vegetables. Studies from the past several years indicate that eating whole foods tends to satisfy hunger and manage weight better than drinking 100% fruit juice, for instance. (23,24,25)

Phytochemicals are certainly not the be all and end all of weight loss. But I think this current research highlights yet another reason why food should be chosen strategically. It is possible to select menu items that you enjoy and that are also tailored to your individual needs. If excess weight is an issue, here’s yet another reason to include more low-glycemic fruits and vegetables in your diet.

Be well!


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5 Comments & Updates to “The Phytochemical Diet”

  1. judi Says:

    What are your thoughts concerning the “new” diet using HCG?
    Thank you for your comments always.

  2. JP Says:


    There’s little new about it, IMO. I’d avoid HCG in all forms.

    Be well!


  3. Ignatius Says:

    It is a good write up on phytochemicals. It is also of note that some components of the plant particularly tannins and pytates can serve as antinutrients.

  4. JP Says:

    Thank you, Ignatius.

    It’s true that certain phytochemicals act as antinutrients. However, their impact on overall nutrient absorption, in the context of a nutrient-dense diet, generally doesn’t trouble me. Simply put, I doubt it makes a major difference in most “real world” circumstances.

    Also, it’s important to note that naturally occurring substances such as phytic acid and tannins possess therapeutic potential independent of their influence on nutrient absorption. Generally speaking, I believe they impart more good than harm.

    Be well!


  5. JP Says:

    Updates: Phytochemical-rich diets support eye function and health …


    Nutr Res. 2014 Dec 31.

    A phytochemical-rich diet may explain the absence of age-related decline in visual acuity of Amazonian hunter-gatherers in Ecuador

    A phytochemical-rich diet may explain the absence of age-related decline in visual acuity of Amazonian hunter-gatherers in Ecuador.
    Myopia is absent in undisturbed hunter-gatherers but ubiquitous in modern populations. The link between dietary phytochemicals and eye health is well established, although transition away from a wild diet has reduced phytochemical variety. We hypothesized that when larger quantities and greater variety of wild, seasonal phytochemicals are consumed in a food system, there will be a reduced prevalence of degenerative-based eye disease as measured by visual acuity. We compared food systems and visual acuity across isolated Amazonian Kawymeno Waorani hunter-gatherers and neighboring Kichwa subsistence agrarians, using dietary surveys, dietary pattern observation, and Snellen Illiterate E visual acuity examinations. Hunter-gatherers consumed more food species (130 vs. 63) and more wild plants (80 vs. 4) including 76 wild fruits, thereby obtaining larger variety and quantity of phytochemicals than agrarians. Visual acuity was inversely related to age only in agrarians (r = -.846, P < .001). As hypothesized, when stratified by age (<40 and ≥ 40 years), Mann-Whitney U tests revealed that hunter-gatherers maintained high visual acuity throughout life, whereas agrarian visual acuity declined (P values < .001); visual acuity of younger participants was high across the board, however, did not differ between groups (P > .05). This unusual absence of juvenile-onset vision problems may be related to local, organic, whole food diets of subsistence food systems isolated from modern food production. Our results suggest that intake of a wider variety of plant foods supplying necessary phytochemicals for eye health may help maintain visual acuity and prevent degenerative eye conditions as humans age.


    Am J Ophthalmol. 2014 Aug;158(2):302-8.

    Adherence to dietary guidelines and the 10-year cumulative incidence of visual impairment: the Blue Mountains Eye Study.


    To assess whether adherence to dietary guidelines at baseline is associated with the incidence of visual impairment among older persons after 10 years.


    A population-based cohort of 3654 participants of the Blue Mountains Eye Study were examined at baseline and were reexamined after 5 and 10 years.


    The incidence of visual impairment was defined as best-corrected visual acuity (VA)<20/40 at follow-up in 1 or both eyes. Dietary information was obtained at baseline using a validated food frequency questionnaire (FFQ). Total Diet Score (TDS) was calculated based on the Australian diet quality index. TDS includes components of diet quality; poor dietary habits; and energy balance. Discrete logistic regression models with time-dependant outcome variables were used to calculate hazard risk ratios (HR) and 95% confidence intervals (CI) associated with incidence of visual impairment for each unit/quartile increase in TDS, adjusting for potential confounders.


    Of the 3654 baseline participants, 1963 had up to 10 years follow-up with completed FFQs. With each unit increase in TDS, the risk of visual impairment decreased (HR 0.94, 95% CI 0.88-1.00). The risk of developing visual impairment was lower among persons in the highest compared to the lowest TDS quartile (HR 0.71, 95% CI 0.47-1.05). This association was significant among persons aged 65+ years (HR 0.63, 95% CI 0.38-0.98) but not those aged <65 years (HR 0.95, 95% CI 0.46-1.97).


    Compliance to dietary guidelines was associated with a decreased long-term risk of visual impairment in this sample of Australians aged 65+ years.

    Be well!


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