Did you ever wonder if the food you eat has a direct effect on your health, well-being – and longevity? Well, I’m here to end that mystery. You ARE the foods you eat. Welcome to the Nutrition Facts podcast – I’m your host, Dr. Michael Greger.
Today, we ask – about the right fruit to eat – the best portion size – and how it should be served. And we start with the exotic lychee fruit – which is actually toxic under certain circumstances.
Lychee fruits have evidently been widely used in many cultures for the folk medicine treatment of everything from farts to testicular swelling. Yeah, but arsenic, mercury, and lead are also included in many “traditional” remedies; so, how much is that really telling us? But lychees have been apparently shown to exhibit numerous health beneﬁts. Yeah, but they cite studies like this. The protective effect of a lychee ﬂower extract on cardiovascular health in a high-fat fed hamster. What are you supposed to do with that? You don’t even eat the flowers and you’re not a hamster. Hard to argue with this, though: a flavor that is sweet, fragrant, and delicious, which is why I love them so much. But then, I saw papers like this: “A child-killing toxin emerges from shadows. Scientists link mystery deaths… to the consumption of lychees.”
In Vietnam, it was called “nightmare” encephalitis—unexplained outbreaks in children coinciding with lychee harvesting. Children go to bed fine, but wake up the next morning seriously ill with brain function derangement and seizures, or they don’t wake up at all. The same thing in India, killing up to nearly two out of three kids affected in some places. And we’re talking thousands of kids, becoming one of the most pressing public health emergencies in the country. It was evidently one of the three long-standing mystery diseases on Wikipedia, remaining a mystery for more than two decades.
All clinical samples were negative for known brain viruses. So, some investigators thought it was caused by some unknown virus; others thought it might have been the pesticides used in the orchards. All we knew is that it seemed to coincide with the lychee harvest. So, maybe the fruit was attracting fruit bats, and then, the mosquitos were transferring some new virus from bats to people. Okay, but then why would toddlers be spared? Mosquitoes bite infants, too.
So, maybe kids were swapping spit with the fruit bats eating half-eaten fruits? Or, maybe it was just because it was summertime, and they were all just getting heat stroke? Okay, then why wasn’t the heat or pesticides affecting adults?
One of the clues that finally helped investigators tease out the mystery was that the children consistently had low blood sugars: in some cases, fatally low blood sugars. That kind of sounds like “Jamaican vomiting sickness.” Perfectly well when they went to bed, but by the next morning, sick, then unconscious, and then, both dead within 48 hours. This is all thanks to eating unripe ackee fruit, which contains a toxin known as hypoglycin, that prevents your liver from churning out blood sugar all night long to keep your brain alive while you sleep. And ackee is a member of the soapberry family, just like lychees. Aha!
But Muzaffarpur is a leading lychee producer, and experts at the National Lychee Center claimed they “completely refuted” the lychee link. But independent researchers found it. Lychee fruit contains methylene cyclopropyl-glycine, a.k.a. the exact same hypoglycin toxin.
So, in the setting of malnourished children who already start out with depleted energy stores in their livers (due to going to bed hungry and general malnutrition), low blood sugar sets in, and due to the excessive lychee consumption, the production of new energy is blocked, and the trouble starts. It’s a social tragedy that children are dying in the 21st century due to low blood sugar, which could be easily corrected. And just as tragic that hungry children are forced to binge on lychees falling on the ground to get a meal. It’s like something out of Grapes of Wrath.
The happy ending, though, is that rather than just focusing on better treatments, public health workers sought instead to treat the cause by educating folks that “no child should go to bed at night without eating a cooked meal, and for parents to restrict children eating lychees in the evening to none or very few”. And thankfully, by applying these recommendations, the disease incidence has been dramatically reduced. In hindsight, it appears China was already warning citizens about the dangers of lychees a decade earlier, but word had apparently just not gotten around.
What are the implications in the West? In the U.S., the FDA tried to protect people against poisoning with this toxin (which is not destroyed by heating) by mandating that canned ackee fruits coming into the country test below a certain level, but there are no such regulations when it comes to importing lychees. “Fortunately, [they figure] the high cost of these imported fruits and the likelihood that they would be eaten in small quantities by well-nourished consumers suggests there is little reason for concern in the USA.” Small quantities? You don’t know how I eat lychees. I used to sneak into movie theaters with big bags of them—pounds of them—because they were just so much fun to peel and eat. How many is too many?
In a series of a few hundred poisoning cases, people reported eating 300 grams to a kilo. Each lychee is about 10 grams; so, that’s 30 to 100 fruit. Most of the cases were in children; so, we can probably safely say 30 to 100 lychees is too many at a time for kids. What about adults? In a self-experiment, a researcher just downed some lychees and measured the hypoglycin levels in his blood and urine. Based on how much was in the fruit, how much he ended up peeing out, and the urine levels found in victims, one can roughly calculate that adults shouldn’t eat more than 200 fresh lychees at a time, or about 10 cans worth.
In our next story we look at how dietary guidelines should stress fresh, frozen, and dried fruit—rather than canned.
Food cans used to be soldered with lead compounds—so much so that people living off of canned food may have died from lead poisoning. Thankfully, this is no longer a problem in the United States. Lead contamination was actually one of the first priorities of the FDA, before it was even called the FDA, back in 1906. It’s great that newspapers now have online archives going back a century, so we can read about landmark historical events like “FDA Proposes Lead-Soldered Cans Be Banned” way back yonder in 1993, going into effect in 1995. Evidently, it was complicated because lead solder was grandfathered in as a prior-sanctioned substance.
Now that the lead is gone, are canned foods healthy? It primarily depends on what’s in the can. If it’s SPAM-dandy, I’d probably pass. Let’s give canned food the benefit of the doubt, though. What about canned fruit?
We know fruits and vegetables in general may help protect us from dying from cardiovascular disease. And when it comes to preventing strokes, fruit may be even more protective. But whether food processing affects this association was unknown. This study found that unprocessed produce (mostly apples and oranges) appeared superior to processed produce. But that was mainly orange and apple juice. No surprise whole fruit is better than fruit juice. What about whole fruit, but just in a can? Dietary guidelines encourage all fruit—fresh, frozen, and canned. But, few studies have examined the health benefits of canned fruit, until now. Canned fruit did not seem able to enable people to live longer. In fact, moving from fresh or dried fruit to canned fruit might even shorten one’s life. So, maybe dietary guidelines should stress fresh, frozen, and dried rather than canned.
Why the difference? There’s no more lead, but there is that plastics chemical—BPA—that is used in the lining of most cans, which can leach into the food, and might counterbalance some of the fruit benefits. Recently, blood levels of this chemical were associated with thickening of the linings of the arteries going up to the brains of young adults, for example. Canned fruit is often packed in syrup, as well, with all that added sugar, and the canning process might diminish some nutrients—potentially wiping out 20% to 40% of the phenolic phytonutrients, and about half of the vitamin C.
Maybe one of the reasons citrus appears particularly protective against stroke is the vitamin C. It appears the more vitamin C in our diet, the lower our risk of stroke; and the more vitamin C in our bloodstream, the lower our risk of stroke. But how did the vitamin C get in our bloodstream? They must have been eating a lot of healthy foods, like citrus, tropical fruits, broccoli, bell peppers.
Therefore, the observed effect of vitamin C on stroke reduction may simply be a proxy for specific healthy foods that lower stroke risk. How could we tell? Give people just vitamin C pills instead and see if they work. They don’t.
Citrus fruits have all sorts of other compounds associated with lower stroke risk. The whole is greater than the sum of its parts. You can’t capture Mother Nature in a pill. It’s like the apocryphal beta-carotene story. Dozens of studies showed that people who ate more beta-carotene-rich foods, like greens and sweet potatoes, and therefore had more beta-carotene circulating in their system, had lower cancer risk. But how much money can we make selling carrots? So, they tried giving people beta carotene pills, and not only did they not work; they may have even caused more cancer.
So, I assumed this National Cancer Institute researcher would conclude the obvious: produce, not pills. But no; maybe we should have tried lower dose pills, or maybe alpha-carotene pills, or pills with other phytochemicals, or multiple combinations. After all, it is likely that neither the public nor the scientific community will be satisfied with recommendations concerned solely with mere foods.
Finally today we ask, does the threshold for toxicity of fructose apply to fruit or just to added industrial sugars such as sucrose and high fructose corn syrup?
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 but 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, thanks to industrial sugars like table sugar and high fructose corn syrup. So, the levels of half of all adults are likely above the threshold for fructose toxicity, 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 by 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 their 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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