Can You Eat Too Much Fruit?

Can You Eat Too Much Fruit?.jpeg

In my video If Fructose is Bad, What About Fruit?, I explored how adding berries to our meals can actually blunt the detrimental effects of high glycemic foods, but how many berries? The purpose of one study out of Finland 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 that 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 dealing with such a crappy breakfast. As you can see in How Much Fruit is Too Much? video, 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 fruit, because they're so healthy--antioxidants, anti-inflammatory, improving artery function, and reducing cancer risk. However, some health professionals have concerns about the sugar content of fruit and therefore recommend restricting the fruit intake. So let's put it to the test! In a study from Denmark, 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 indeed reduce their fruit consumption, but it had no effect on the control of their diabetes or weight, and so, the researchers concluded, 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. 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, 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 ten in a piece of fruit, should we not eat more than five fruit 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 fruit a day? How about twenty fruit a day?

It's actually been put to the test.

Seventeen people were made to eat 20 servings a day of fruit. Despite the extraordinarily high fructose content of this diet, presumably about 200 g/d--eight cans of soda worth, the investigators reported no adverse effects (and possible benefit actually) for body weight, blood pressure, and insulin and lipid levels after three to six months. More recently, Jenkins and colleagues put people on about a 20 servings of fruit a day diet for a few weeks and found 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 bowl movements apparently ever documented in a dietary intervention.


Cutting down on sugary foods may be easier said than done (see Are Sugary Foods Addictive?) but it's worth it. For more on the dangers of high levels of fructose in added sugars, see How Much Added Sugar Is Too Much?.

What's that about being in oxidative debt? See my three part series on how to pull yourself out of the red:

Ironically, fat may be more of a problem when it comes to diabetes than sugar, see:

In health,
Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Image Credit: Sally Plank / Flickr. This image has been modified.

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Can You Eat Too Much Fruit?

Can You Eat Too Much Fruit?.jpeg

In my video If Fructose is Bad, What About Fruit?, I explored how adding berries to our meals can actually blunt the detrimental effects of high glycemic foods, but how many berries? The purpose of one study out of Finland 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 that 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 dealing with such a crappy breakfast. As you can see in How Much Fruit is Too Much? video, 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 fruit, because they're so healthy--antioxidants, anti-inflammatory, improving artery function, and reducing cancer risk. However, some health professionals have concerns about the sugar content of fruit and therefore recommend restricting the fruit intake. So let's put it to the test! In a study from Denmark, 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 indeed reduce their fruit consumption, but it had no effect on the control of their diabetes or weight, and so, the researchers concluded, 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. 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, 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 ten in a piece of fruit, should we not eat more than five fruit 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 fruit a day? How about twenty fruit a day?

It's actually been put to the test.

Seventeen people were made to eat 20 servings a day of fruit. Despite the extraordinarily high fructose content of this diet, presumably about 200 g/d--eight cans of soda worth, the investigators reported no adverse effects (and possible benefit actually) for body weight, blood pressure, and insulin and lipid levels after three to six months. More recently, Jenkins and colleagues put people on about a 20 servings of fruit a day diet for a few weeks and found 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 bowl movements apparently ever documented in a dietary intervention.


Cutting down on sugary foods may be easier said than done (see Are Sugary Foods Addictive?) but it's worth it. For more on the dangers of high levels of fructose in added sugars, see How Much Added Sugar Is Too Much?.

What's that about being in oxidative debt? See my three part series on how to pull yourself out of the red:

Ironically, fat may be more of a problem when it comes to diabetes than sugar, see:

In health,
Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Image Credit: Sally Plank / Flickr. This image has been modified.

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Why Smoothies are Better Than Juicing

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Studies such as a recent Harvard School of Public Health investigation found that the consumption of whole fruits is associated with a significantly lower risk of type 2 diabetes, whereas fruit juice consumption is associated with a higher risk, highlighting the dramatic difference between eating whole fruits and drinking fruit juice. Cholesterol serves as another example. If we eat apples, our cholesterol drops. On the other hand, if we drink apple juice, our cholesterol may actually go up a little. Leaving just a little of the fiber behind--as in cloudy apple juice--was found to add back in some of the benefit.

We used to think of fiber as just a bulking agent that helps with bowel regularity. We now know fiber is digestible by our gut bacteria, which make short chain fatty acids (SCFAs) out of it. SCFAs have a number of health promoting effects, such as inhibiting the growth of bad bacteria and increasing mineral absorption. For example, experimentally infused into the rectum of the human body, SCFAs can stimulate calcium absorption, so much so that we can improve the bone mineral density of teenagers just by giving them the fiber naturally found in foods like onions, asparagus, and bananas.

Our good bacteria also uses fiber to maintain normal bowel structure and function, preventing or alleviating diarrhea, stimulating colonic blood flow up to five-fold, and increasing fluid and electrolyte uptake. The major fuel for the cells that line our colon is butyrate, which our good bacteria make from fiber. We feed them, and they feed us right back.

If the only difference between fruit and fruit juice is fiber, why can't the juice industry just add some fiber back to the juice? The reason is because we remove a lot more than fiber when we juice fruits and vegetables. We also lose all the nutrients that are bound to the fiber.

In the 1980's, a study (highlighted in my video, Juicing Removes More Than Just Fiber) found a discrepancy in the amount of fiber in carob using two different methods. A gap of 21.5 percent was identified not as fiber but as nonextractable polyphenols, a class of phytonutrients thought to have an array of health-promoting effects. Some of the effects associated with the intake of dietary fiber in plants may actually be due to the presence of these polyphenols.

Nonextractable polyphenols, usually ignored, are the major part of dietary polyphenols. Most polyphenol phytonutrients in plants are stuck to the fiber. These so-called missing polyphenols make it down to our colon, are liberated by our friendly flora and can then get absorbed into our system. The phytonutrients in fruit and vegetable juice may just be the tip of the iceberg.

For those that like drinking their fruits and vegetables, these findings suggest that smoothies may be preferable. I can imagine people who eat really healthy thinking they get so much fiber from their regular diet that they need not concern themselves with the loss from juicing. But we may be losing more than we think.

For those that like drinking their fruits and vegetables, this suggests smoothies are preferable. I can imagine people who eat really healthy thinking they get so much fiber from their regular diet that they need not concern themselves with the loss from juicing, but they may be losing more than they think.

Why are polyphenol phytonutrients important? See, for example, my video How to Slow Brain Aging by Two Years

Not that fiber isn't important in its own right. Check out:

For more on smoothies, check out:

In health,
Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, From Table to Able, and Food as Medicine.

Image Credit: Craig Sunter / Flickr

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Don’t Forget Fiber

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The famous surgeon Denis Burkitt is better known for his discovery of a childhood cancer now known as Burkitt's lymphoma than for his 1979 international bestseller, Don't Forget the Fibre in Your Diet.

Anyone asked to list the twenty or more most important advances in health made in the last few decades would be likely to include none of what Dr. Burkitt considered to be among the most significant. What was the number one most important advance in health according to one of the most famous medical figures of the 20th century? The discovery that "Many of the major and commonest diseases in modern Western culture are universally rare in third-world communities, were uncommon even in the United States until after World War l" yet are now common in anyone following the Western lifestyle. So it's not genetics--they're lifestyle diseases (See Dr. Burkitt's F-Word Diet). This means they must potentially be preventable.

Those eating the standard American diet have very high levels of a long list of diseases--such as heart disease and colon cancer--that were similar to the rates of disease in the ruling white class in apartheid Africa. Conversely, the rates in the Bantu population were very low. These native Africans ate the same three sister diets of many Native Americans, a plant-based diet centered around corn, beans, and squash. In fact, it was reported that cancer was so seldom seen in American Indians a century ago they were considered practically immune to cancer--and heart disease. What are "very low" rates? 1300 Bantus were autopsied over five years in a Bantu hospital and maybe one case of ischemic heart disease, the West's number one killer.

The Bantu's rates of heart and intestinal disease is similar to poor Indians, whereas wealthier Indians who ate more animal and refined foods were closer to those in Japan--unless they moved to the U.S. and started living like us. You find similar trends for the other so-called Western diseases, which Burkitt thought were related to the major dietary changes that followed the lndustrial Revolution: a reduction in healthy whole plant foods--the source of starch and fiber-and a great increase in consumption of animal fats, salt, and sugar. His theory was that it was the fiber. He believed all of these major diseases may be caused by a diet deficient in whole plant foods, the only natural source of fiber.

Fiber? In a survey of 2,000 Americans, over 95% of graduate school-educated participants and health care providers weren't even aware of the daily recommended fiber intake. Doctors don't even know. How much fiber should we shoot for? The Institute of Medicine recommends 38 grams for men 50 years and younger and 30 grams for men over 50 years. Women 50 years and younger should get 25 and those older than 50 should get 21 grams. But these levels are just the minimum. I recommend we look to our evolutionary past for more clues on fiber intake. See my video Paleolithic Lessons.

One analogy Dr. Burkitt used is this: "If a floor is flooded as a result of a dripping tap, it is of little use to mop up the floor unless the tap is turned off. The water from the tap represents the cause of disease, the flooded floor the diseases filling our hospital beds. Medical students learn far more about methods of floor mopping than about turning off taps, and doctors who are specialists in mops and brushes can earn infinitely more than those dedicated to shutting off taps." And the drug companies is more than happy to sell us rolls of paper towels, so patients can buy a new roll every day for the rest of their lives. To paraphrase Ogden Nash: modern medicine is making great progress, but just headed in the wrong direction.

How do we know that diet was the critical factor? Because when we place people stricken with these diseases on plant-based diets, their disease can be reversed (Our Number One Killer Can Be Stopped). In fact it was the work of Burkitt and others in Africa that led to the disease reversal work of pioneers like Nathan Pritikin (Engineering a Cure).

More on fiber:

And for more of the scoop on poop:

-Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, and From Table to Able.

Image Credit: Rachel Hathaway / Flickr

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We Can End the Heart Disease Epidemic

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Many of the diseases that are common in United States are rare or even nonexistent in populations eating mainly whole plant foods.

These so-called Western Diseases are some of our most common conditions:

  • Obesity, the most important nutritional disease
  • Hiatal hernia, one of the most common stomach problems
  • Hemorrhoids and varicose veins, the most common venous disorders
  • Colorectal cancer, the number two cause of cancer death
  • Diverticulosis, the #1 disease of the intestine
  • Appendicitis, the #1 cause for emergency abdominal surgery
  • Gallbladder disease, the #1 cause for nonemergency abdominal surgery
  • Ischemic heart disease, the #1 cause of death

These diseases are common in the West, but are rarities among plant-based populations.

A landmark study in 1959 I profiled in my video Cavities and Coronaries: Our Choice, for example, suggested that coronary heart disease was practically non-existent among those eating traditional plant-based diets in Uganda.

"Doctors in sub-Saharan Africa during the '30s and '40s recognized that certain diseases commonly seen in Western communities were rare in rural African peasants. This hearsay talk greeted any new doctor on arrival in Africa. Even the teaching manuals stated that diabetes, coronary heart disease, appendicitis, peptic ulcer, gallstones, hemorrhoids, and constipation were rare in African blacks who eat foods that contain many skins and fibers, such as beans and corn, and pass a bulky stool two or three times a day. Surgeons noticed that the common acute abdominal emergencies in Western communities were virtually absent in rural African peasants."

But did they have hard data to back it up? Yes.

Major autopsy series were performed. In one thousand Kenyan autopsies, there were "no cases of appendicitis, not a single heart attack, only three cases of diabetes, one peptic ulcer, no gallstones, and no evidence of high blood pressure" (which alone affects one out of three Americans).

Maybe the Africans were just dying early of other diseases and so never lived long enough to get heart disease? No. In the video One in a Thousand: Ending the Heart Disease Epidemic, you can see the age-matched heart attack rates in Uganda versus St. Louis. Out of 632 autopsies in Uganda, only one myocardial infarction. Out of 632 Missourians--with the same age and gender distribution--there were 136 myocardial infarctions. More than 100 times the rate of our number one killer. In fact, researchers were so blown away that they decided to do another 800 autopsies in Uganda. Still, just that one small healed infarct (meaning it wasn't even the cause of death) out of 1,427 patients. Less than one in a thousand, whereas in the U.S., it's an epidemic.

If heart disease is so rare in rural Africa, how do the local doctors even know what to look for? Though practically unheard of among the native population, the physicians are quite familiar with heart disease because of all the Westerners that immigrate to the country.

The famous surgeon Dr. Denis Burkitt insisted that modern medicine is treating disease all wrong:

"A highly unacceptable fact--that is rarely considered yet indisputable--is that, with rare exceptions, there is no evidence that the incidence of any disease was ever reduced by treatment. Improved therapies may reduce mortality but may not reduce the incidence of the disease."

Take cancer, for example, where the vast majority of effort is devoted to advances in treatment, and second priority is given to screening programs attempting early diagnosis. Is there any evidence that the incidence of any form of cancer has been reduced by improved treatment or by early detection? Early diagnosis may reduce mortality rates, and medical services can have a profoundly beneficial effect on sick people, but neither have little (if any) effect on the number of people becoming ill. No matter how fancy heart disease surgery gets, it's never going to reduce the number of people falling victim to the disease.

Dr. Burkitt compared the situation to an engine left out in the rain:

"If an engine repeatedly stops as a consequence of being exposed to the elements, it is of limited value to rely on the aid of mechanics to detect and remedy the fault. Examination of all engines would reveal that those out in the rain were stopping, but those under cover were running well. The correct approach would then be to provide protection from the offending environment. However, considering the failing engine as the ailing patient, this is seldom the priority of modern medicine."

Dr. Burkitt sums it up with the analogy of The Cliff or the Ambulance:

"If people are falling over the edge of a cliff and sustaining injuries, the problem could be dealt with by stationing ambulances at the bottom or erecting a fence at the top. Unfortunately, we put far too much effort into the provision of ambulances and far too little into the simple approach of erecting fences."

And of course there are all the industries enticing people to the edge, and profiting from pushing people off.

If all plant-based diets could do is reverse our number one killer, then shouldn't that be the default diet until proven otherwise? The fact that it also appears to reverse other leading killers like diabetes and hypertension appears to make the case for plant-based eating overwhelming. So why doesn't the medical profession embrace it? It may be because of The Tomato Effect. Why don't many individual doctors do it? It may be because lifestyle medicine hurts the bottom line (see Lifestyle Medicine: Treating the Causes of Disease). Why doesn't the federal government recommend it? It may be because of the self-interest of powerful industries (see The McGovern Report). But you can take your destiny into your own hands (mouth?) and work with your doctor to clean up your diet and maximize your chances of living happily ever after.

-Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, and From Table to Able.

Image Credit: Sinn Fien / Flickr

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