by Craig Weatherby
This week brought news that underlines the dangers of America’s sugary, starchy diets… but led us to evidence that colorful plant foods can blunt some effects of junky foods.
First, let’s hear the bad news.
The antioxidant capacity of blood is a measure of its ability to control the potentially damaging “pro-oxidant” compounds called free radicals.
Why does this seemingly arcane blood measurement matter?
As the Children’s Hospital researchers wrote, “Oxidative stress, caused by an imbalance between antioxidant capacity and reactive oxygen species [free radicals], may be an early event in a metabolic cascade elicited by a high glycemic index (GI) diet, ultimately increasing the risk for cardiovascular disease and diabetes” (Botero D et al. 2009).
By “high-glycemic”, they mean a diet high in sugars and starches that produce rapid, steep rises in blood sugar levels… an effect that, over time, can lead to diabetes.
In other words, sugary, starchy, high-GI diets yield lots of free radicals, which damage cells and promote inflammation. As a result, an excess of free radicals increases your risk for cardiovascular disease and diabetes.
The Boston-based doctors enrolled 12 overweight or obese men aged 18-35, and assigned them either to a diet with a low glycemic index (GI) rating or a high-GI rating.
A week later, they measured the total antioxidant capacity (AOC) of the men’s blood, and on day 10 they measured cardiovascular disease risk factors in their blood.
As they reported, “…total antioxidant capacity was significantly higher during the low-GI vs. high-GI diet...” (Botero D et al. 2009).
In other words, diets low in sugars and refined starches left the men’s bodies better able to prevent the ravages of uncontrolled free radicals.
This outcome prompted us to look for anti-sugar measures… and we found encouragement in clinical results published jointly by scientists from the USDA, UC Davis and the University of Maine.
This team set out to tackle a key question: Does it matter when you eat colorful, antioxidant-rich plant foods?
The answer, as it turns out, is “yes”.
Before we review that study’s outcomes with regard to timing of antioxidant intake, let’s review the reasons why dietary antioxidants matter.
Free radicals, antioxidants, and aging
When unstable oxygen molecules called “free radicals” grab electrons from the chemical compounds that form our cells’ membranes, energy centers (mitochondria), and genetic material (RNA and DNA) that common chemical reaction is called “oxidation”.
Oxidation is the same chemical process that rusts iron, and it is an important driver of aging and disease.
Free radicals are a normal byproduct of food metabolism… but these pro-oxidants get created in excess when we consume refined carbohydrates (sugars and white starches), and that excess can overwhelm the body’s internal antioxidant network.
Our bodies’ own network of antioxidants usually controls free radicals pretty well, but the excess generated by eating starchy, sugary foods can overwhelm that system.
Uncontrolled free radicals can damage the linings of our arteries and promote the inflammation that underlies and drives major degenerative diseases from Alzheimer’s, cancer, cataracts, and macular degeneration to diabetes.
Meals high in sugars and starches generate swarms of free radicals and downstream inflammatory effects in the body. And browned bread crusts and meats contain sugar-protein compounds that generate free radicals and inflammation.
Thankfully, the available lab and clinical research suggests that the antioxidants in whole grains and colorful plant foods such as berries and greens can help control meal-generated free radicals (Natella F et al. 2002; Kay CD et al. 2002; Mazza G et al. 2002; Ko SH et al. 2005).
In addition, plant-borne antioxidants exert generally anti-inflammatory influences over cellular genetic switches called transcription factors (see “Food-Borne Antioxidants May Act Indirectly”).
But the USDA-UC-Maine team’s findings point to timing as a factor in the ability of antioxidant-rich foods to control the free radicals generated when we eat meats, dairy, sugars, and refined fats and starches… which lack the antioxidants abundant in whole plant foods (i.e., vitamins C and E and various phytochemicals).
Clinical tests find timing critical to a key benefit of food-borne antioxidants
Researchers from the US Department of Agriculture (USDA) measured the blood antioxidant capacity (AOC) of subjects in a series of five clinical trials.
They found that antioxidant-rich foods blunted the oxidative stress generated by eating meals high in protein and refined carbohydrates and fats (Prior RL et al. 2007).
When the participants ate antioxidant-rich fruits—such as blueberries, grapes, and kiwifruit—the antioxidant capacity of their blood rose during the critical few hours following a meal.
But those antioxidant-rich foods reduced oxidation the most when they were eaten as part of a meal… or soon thereafter.
Conversely, participants who consumed protein, carbohydrates, and fats without substantial antioxidants showed a decline in the blood’s antioxidant capacity (AOC).
In other words, the results indicated two things:
- Consuming antioxidant-rich foods during meals reduces the oxidative stress associated with eating.
- Timing is important, because the antioxidants in colorful plant foods don’t linger very long in the blood.
To get this data, the researchers conducted five clinical trials with six to 10 subjects per experiment. Blood samples were taken from the subjects before and after they ate a prescribed meal, to measure their blood’s AOC.
Eating blueberries or grapes with a meal yielded an increase in water-soluble AOC, while blueberries also increased the fat-soluble AOC of participants’ blood.
Cherries eaten with the meal increased the fat-soluble, but not the water-soluble AOC of participants’ blood.
Surprisingly, neither prunes (dried plums) nor prune juice altered either measure of antioxidant activity, despite plums’ high ranking on the standard ORAC scale.
The ORAC scale is based on test tube measurements, so scientists at Cornell University propose a new measure of antioxidant activity called the cellular antioxidant activity (CAA) assay, which tests antioxidant compounds’ activity inside cells (See “Wild Blueberries Reclaim Antioxidant Crown”).
As expected, eating a meal low in antioxidants—animal protein plus refined carbs and fats—cut participants’ blood AOC and produced an increase in oxidative stress.
Lead author Ronald Prior said it’s not just what you eat but when you eat it that matters: “Phytochemicals in foods have varying degrees of bioavailability and generally are cleared from the blood 2-4 hours after they're eaten. Ensuring that your body has a steady supply of antioxidant-rich foods can help combat oxidative stress throughout the day” (WBA 2007).
And he went on to add this important note on the quantity of antioxidant-rich foods needed to yield measureable effects on someone’s blood AOC:
“The more calories you take in the more dietary antioxidants you need. It takes about 2.5 servings of antioxidant containing fruits and/or vegetables in a meal… to prevent oxidative stress following the meal.” (WBA 2007)
The USDA-UC-Maine team appended an important caveat: “Without further long term clinical studies, one cannot necessarily translate increased plasma [blood] AOC into a potential decreased risk of chronic degenerative disease” (Prior RL et al. 2007).
The research was funded by the Wild Blueberry Association of Maine, but it seems unlikely the highly experienced, credible USDA team was influenced by this link.
- Botero D, Ebbeling CB, Blumberg JB, Ribaya-Mercado JD, Creager MA, Swain JF, Feldman HA, Ludwig DS. Acute effects of dietary glycemic index on antioxidant capacity in a nutrient-controlled feeding study. Obesity (Silver Spring). 2009 Sep;17(9):1664-70. Epub 2009 Jun 18.
- Kay CD, Holub BJ. The effect of wild blueberry (Vaccinium angustifolium) consumption on postprandial serum antioxidant status in human subjects. Br J Nutr. 2002 Oct;88(4):389-98.
- Ko SH, Choi SW, Ye SK, Cho BL, Kim HS, Chung MH. Comparison of the antioxidant activities of nine different fruits in human plasma. J Med Food. 2005 Spring;8(1):41-6.
- Mazza G, Kay CD, Cottrell T, Holub BJ. Absorption of anthocyanins from blueberries and serum antioxidant status in human subjects. J Agric Food Chem. 2002 Dec 18;50(26):7731-7.
- Natella F, Belelli F, Gentili V, Ursini F, Scaccini C. Grape seed proanthocyanidins prevent plasma postprandial oxidative stress in humans. J Agric Food Chem. 2002 Dec 18;50(26):7720-5.
- Prior RL, Gu L, Wu X, Jacob RA, Sotoudeh G, Kader AA, Cook RA. Plasma antioxidant capacity changes following a meal as a measure of the ability of a food to alter in vivo antioxidant status. J Am Coll Nutr. 2007 Apr;26(2):170-81.
- Wild Blueberry Association of North America (WBA). USDA Study Examines Antioxidant Status Changes After Meals. Nov. 30, 2007. Accessed at http://www.bio-medicine.org/medicine-news-1/Wild-Blueberries-Shown-to-Fight-Oxidative-Stress-7299-1/