Flashback Friday: How Much Fruit Is Too Much?

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Previously, I explored how adding blueberries to our meals can actually blunt the detrimental effects of high glycemic foods; but how many berries? The purpose was to determine the minimum level of blueberry consumption at which a consumer may realistically expect to receive antioxidant benefits after eating blueberries with a sugary breakfast cereal. If we eat a bowl of corn flakes with no berries, within two hours, so many free radicals are created it puts us into oxidative debt. The antioxidant power of our bloodstream drops below where we started from before breakfast as the antioxidants in our bodies get used up. And a quarter cup of blueberries didn’t seem to help much. But a half cup of blueberries did.

What about fruit for diabetics? Most guidelines recommend eating a diet with a high intake of fiber-rich food including fruits, because they’re so healthy—antioxidants, anti-inflammatory, improve artery function and reduce cancer risk. However, some health professionals have concerns about the sugar content of fruit, and therefore recommend restricting the fruit intake. OK, let’s put it to the test. Diabetics were randomized into two groups–one told to eat at least two pieces of fruit a day, and the other told at most, two fruits a day. The reduce fruit group reduced their fruit. It had, however, no effect on the control of their diabetes or weight–”and so the intake of fruit should not be restricted in patients with type 2 diabetes.”

An emerging literature has shown that low-dose fructose may actually benefit blood sugar control. So having a piece of fruit with each meal would be expected to lower, not raise, the blood sugar response. The threshold for toxicity of fructose may be around 50 grams. The problem is that’s the current average adult fructose consumption. So the levels of half of all adults are likely above the threshold for fructose toxicity, thanks to industrial sugars like table sugar and high fructose corn syrup, and adolescents currently average 75.

Is that limit for added sugars or for all fructose? If we don’t want more than 50, and there’s about 10 in a piece of fruit, should we not eat more than five fruits a day? Quoting from the Harvard Health Letter, “The nutritional problems of fructose and sugar come when they are added to foods. Fruit, on the other hand, is beneficial in almost any amount.” What do they mean almost? Can we eat ten fruits a day? How about twenty fruits a day? It’s actually been put to the test.

Seventeen people were made to eat twenty servings a day of fruit. Despite the extraordinarily high fructose content of this diet, presumably about 200 grams a day—8 cans of soda worth—the investigators reported no adverse effects (and possible benefit actually) for body weight, blood pressure, and insulin and lipid levels (fats in the blood) after three to six months. More recently, Jenkins and colleagues put people on about a twenty-servings-of-fruit-a-day diet for a few weeks, and no adverse effects on weight or blood pressure or triglycerides, and an astounding 38-point drop in LDL cholesterol.

There was one side effect, though. Given the 44 servings of vegetables they had on top of all that fruit, they recorded the largest bowel movements apparently ever documented in a dietary intervention.

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• R Törrönen, M Kolehmainen, E Sarkkinen, K Poutanen, H Mykkänen, L Niskanen. Berries reduce postprandial insulin responses to wheat and rye breads in healthy women. J Nutr. 2013 Apr;143(4):430-6.
• A S Christensen, L Viggers, K Hasselström, S Gregersen. Effect of fruit restriction on glycemic control in patients with type 2 diabetes--a randomized trial. Nutr J. 2013 Mar 5;12:29.
• B C Blacker, S M Snyder, D L Eggett, T L Parker. Consumption of blueberries with a high-carbohydrate, low-fat breakfast decreases postprandial serum markers of oxidation. Br J Nutr. 2013 May;109(9):1670-7.
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• D S Ludwig. Examining the health effects of fructose. JAMA. 2013 Jul 3;310(1):33-4.
• R H Lustig. Fructose: it's "alcohol without the buzz". Adv Nutr. 2013 Mar 1;4(2):226-35.
• B J Meyer, E J de Bruin, D G Du Plessis, M van der Merwe, A C Meyer. Some biochemical effects of a mainly fruit diet in man. S Afr Med J. 1971 Mar 6;45(10):253-61.
• D J Jenkins, C W Kendall, D G Popovich, E Vidgen, C C Mehling, V Vuksan, T P Ransom, A V Rao, R Rosenberg-Zand, N Tariq, P Corey, P J Jones, M Raeini, J A Story, E J Furumoto, D R Illingworth, A S Pappu, P W Connelly. Effect of a very-high-fiber vegetable, fruit, and nut diet on serum lipids and colonic function. Metabolism. 2001 Apr;50(4):494-503.

Images thanks to vic xia via flickr