Getting a hearty dose of fruits and veggies is great for overall health.
And that's especially true if you're watching your waistline and trying to deter diabetes.
To be sure, fiber plays an important part in veggies' ability to help fight weight gain.
But it looks like the antioxidants in certain fruits and veggies are overlooked allies.
And new research from Harvard suggest that differences in their antioxidant profiles make some fruits and vegetables particularly potent weight control allies.
Harvard study detects key differences among veggies
A team led by Harvard researchers analyzed the dietary habits of more than 124,000 American adults (Bertoia ML et al. 2016).
The participating men and women were volunteers in three super-sized epidemiological studies: The Health Professionals Follow-up Study (HPFS), the Nurses' Health Study (NHS), and the Nurses' Health Study II (NHS II).
The Harvard led team focused on several different kinds of flavonoid-type antioxidants … a family that includes several distinct sub-groups.
The scientists wanted to find out whether different kinds of flavonoid antioxidants had different impacts on weight control.
As they said, "Most weight loss studies to date have focused on the flavan-3-ol subclass [of flavonoids] found in green tea and are limited to small numbers of overweight and obese participants.”
In contrast, their study was the first to look for links between weight gain and all three major subclasses of flavonoids commonly found in fruits and vegetables (flavonols, anthocyanins, and flavones).
Different fruits and vegetables have different "antioxidant profiles”, which means that they contain greater or smaller proportions of the various kinds of flavonoids.
(Many fruits and vegetables also contain carotenoid-type antioxidants, such as the beta-carotene in yellow-red fruits and vegetables, and the xanthophylls in leafy greens, shrimp, and wild salmon. This study did not compare the carotenoid content of participants' diets to their weight loss or gain history.)
To do that, they compared people's self-reported changes in weight to their self-reported consumption of various fruits and vegetables during several four-year intervals between 1986 and 2011.
In a nutshell, they found that the people who consumed the most flavonoids gained the least weight over time.
Those results held true even after the researchers adjusted for other factors that impact weight, such as smoking, fiber intake, and physical activity.
But which flavonoids (and source foods) were linked to the least weight gain?
Study revealed the most effective flavonoids for weight control
The diets richest in three kinds of flavonoids – flavonols, flavan-3-ols, anthocyanins, and flavonoid polymers – were linked to the lowest risk of weight gain.
(The most common flavonoid polymers are proanthocyanidins, which abound in berries, unprocessed cocoa, and extra-dark chocolate.)
Overall, each extra daily portion of produce rich in these three subgroups of flavonoids was linked to the gain of 0.16 to 0.23 fewer pounds over the course of each year, compared with participants who didn't consume as much of these flavonoids.
In other words, that level of flavonoid consumption would keep you from gaining five pounds over the course of several years … And would provide the powerful health benefits associated with diets rich in flavonoids.
What were the main food sources of these most beneficial flavonoids?
- Flavonols: Tea and onions
- Flavan-3-ols: Tea and apples.
- Anthocyanins: Blueberries and strawberries
- Flavanones and flavones: Orange juice and oranges
It's important to note that this list doesn't necessarily include the richest sources of the most effective flavonoids.
Instead, it simply lists the fruits and vegetables from which the participants derived most of these beneficial flavonoids.
For example, coffee ranks high among all sources of flavon-3-ols, with more than green or black tea. But coffee doesn't count as a fruit or vegetable. Coffee also contains more caffeine, which is a proven aid to calorie burning.
Likewise, unprocessed cocoa and extra-dark chocolate are also extremely rich in flavon-3-ols, and rank as the richest food sources ... but the study didn't count either one as a source of these flavonoids.
Why would colorful fruits and veggies aid weight control?
The Harvard led team suggested that research on tea – which is very rich in flavon-3-ol type flavonoids – may help explain their findings.
For example, European researchers recently reported that flavonoid-rich green tea blocks the digestion of starch and fat. (Walkowiak J et al. 2013; Lochocka K et al. 2015).
And it's long been known that the flavonoids in green tea promote calorie burning … especially the burning of body fat for energy (Dulloo AG et al. 1999; Gregersen NT et al. 2009)
Results echo prior findings
This isn't the first piece of research to link fruit and vegetable consumption to a lowered risk of weight gain.
A previous study from the Harvard School of Public Health found that eating more fruits and veggies high in fiber but low in carbs – think apples, pears, string beans and dark leafy greens like spinach – lowered the risk of weight gain.
On the other hand, they linked diets high in starchy vegetables like potatoes, corn and peas to weight gain.
Starchy vegetables have a higher "glycemic load”, meaning they tend to produce a spike in blood sugar after they're consumed.
Sharp rises in blood sugar lead to later bouts of hunger. In contrast, high-fiber fruits and veggies don't produce blood sugar spikes.
Another large Harvard study, published four years ago, linked higher consumption of anthocyanin-rich fruits (mostly berries) to a reduced risk for developing diabetes (Wedick NM et al. 2012).
Even though the fruits were fairly high in sugars, their potentially bad impact on blood sugar was effectively counteracted by their antioxidant flavonoids.
Fruit juices contain much higher levels of sugar compared their antioxidant content.
Nonetheless, the new Harvard study suggest that moderate consumption of fruit juices may aid weight control.
But it's much healthier to consume whole fruits and vegetables than to guzzle their juices.
How should we act on these findings?
According to the Harvard-led team, most of us are currently missing the mark with our diets.
The majority of Americans consume less than one cup (two servings) of fruit and less than two cups (about three servings) of vegetables daily.
What's worse, most of these servings come from sugar-laden juices or starchy vegetables.
Instead, we should aim for at least two cups of fruit and two and a half cups of vegetables each day.
And choose wisely to reap the biggest waist-saving benefits.
According to the Harvard researchers and Oregon State University, these are the richest sources of the best flavonoids for weight control:
Apples, pears, berries, onions, peppers, red/purple grapes, scallions, kale, broccoli, parsley, thyme, celery, chili peppers, and whole citrus fruits (oranges, grapefruits, lemons), and cocoa (non-alkalized/non-Dutched).
Fortunately, red wine also make the list, as does extra-dark chocolate … that is, chocolate with 80% or more cocoa.
- Bertoia ML, Rimm EB, Mukamal KJ, Hu FB, Willett WC, Cassidy A. Dietary flavonoid intake and weight maintenance: three prospective cohorts of 124 086 US men and women followed for up to 24 years. BMJ. 2016 Jan 28;352:i17. doi: 10.1136/bmj.i17.
- Dulloo AG, Duret C, Rohrer D, Girardier L, Mensi N, Fathi M, Chantre P, Vandermander J. Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans. Am J Clin Nutr. 1999 Dec;70(6):1040-5.
- Gregersen NT, Bitz C, Krog-Mikkelsen I, Hels O, Kovacs EM, Rycroft JA, Frandsen E, Mela DJ, Astrup A. Effect of moderate intakes of different tea catechins and caffeine on acute measures of energy metabolism under sedentary conditions. Br J Nutr. 2009 Oct;102(8):1187-94. doi: 10.1017/S0007114509371779. Epub 2009 May 18.
- Lochocka K, Bajerska J, Glapa A, Fidler-Witon E, Nowak JK, Szczapa T, Grebowiec P, Lisowska A, Walkowiak J. Green tea extract decreases starch digestion and absorption from a test meal in humans: a randomized, placebo-controlled crossover study. Sci Rep. 2015 Jul 30;5:12015. doi: 10.1038/srep12015.
- Oregon State University/ Linus Pauling Institute. Flavonoids. Accessed at http://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/flavonoids
- USDA Agricultural Research service. Phytonutrient FAQs. Accessed at http://www.ars.usda.gov/aboutus/docs.htm?docid=4142#classes
- Walkowiak J, Bajerska J, Kargulewicz A, Lisowska A, Siedlerski G, Szczapa T, Kobelska-Dubiel N, Grzymisławski M. Single dose of green tea extract decreases lipid digestion and absorption from a test meal in humans. Acta Biochim Pol. 2013;60(3):481-3. Epub 2013 Aug 29.
- Wedick NM, Pan A, Cassidy A, Rimm EB, Sampson L, Rosner B, Willett W, Hu FB, Sun Q, van Dam RM. Dietary flavonoid intakes and risk of type 2 diabetes in US men and women. Am J Clin Nutr. 2012 Apr;95(4):925-33. doi: 10.