What Exercise Authorities Don’t Tell You About Optimal Duration

Physical fitness authorities seem to have fallen into the same trap as the nutrition authorities, recommending what they think may be achievable, rather than simply informing us of what the science says and letting us make up our own minds.

Researchers who accept grants from The Coca-Cola Company may call physical inactivity “the biggest public health problem of the 21st century,” but, in actually, physical inactivity ranks down at number five in terms of risk factors for death in the United States and even lower in terms of risk factors for disability, as you can see at 0:17 in my video How Much Should You Exercise? What’s more, inactivity barely makes the top ten globally. As we’ve learned, diet is our greatest killer by far, followed by smoking.

Of course, that doesn’t mean you can just sit on the couch all day. Exercise can help with mental health, cognitive health, sleep quality, cancer prevention, immune function, high blood pressure, and life span extension, topics I cover in some of my other videos. If the U.S. population collectively exercised enough to shave just 1 percent off the national body mass index, 2 million cases of diabetes, one and a half million cases of heart disease and stroke, and 100,000 cases of cancer might be prevented.

Ideally, how much should we exercise? The latest official “Physical Activity Guidelines for Americans” recommends adults get at least 150 minutes a week of moderate aerobic exercise, which comes out to be a little more than 20 minutes a day. That is actually down from previous recommendations from the Surgeon General, as well as from the Centers for Disease Control and Prevention (CDC) and the American College of Sports Medicine, which jointly recommend at least 30 minutes each day. The exercise authorities seem to have fallen into the same trap as the nutrition authorities, recommending what they think may be achievable, rather than simply informing us what the science says and letting us make up our own minds. They already emphasize that “some” physical activity “is better than none,” so why not stop patronizing the public and just tell everyone the truth?

As you can see at 2:16 in my video, walking 150 minutes a week is better than walking 60 minutes a week, and following the current recommendations for 150 minutes appears to reduce your overall mortality rate by 7 percent compared with being sedentary. Walking for just 60 minutes a week only drops your mortality rate about 3 percent, but walking 300 minutes weekly lowers overall mortality by 14 percent. So, walking twice as long—40 minutes a day compared with the recommended 20 daily minutes—yields twice the benefit. And, an hour-long walk each day may reduce mortality by 24 percent. I use walking as an example because it’s an exercise nearly everyone can do, but the same applies to other moderate-intensity activities, such as gardening or cycling.

A meta-analysis of physical activity dose and longevity found that the equivalent of about an hour a day of brisk walking at four miles per hour was good, but 90 minutes was even better. What about more than 90 minutes? Unfortunately, so few people exercise that much every day that there weren’t enough studies to compile a higher category. If we know 90 minutes of exercise a day is better than 60 minutes, which is better than 30 minutes, why is the recommendation only 20 minutes? I understand that only about half of Americans even make the recommended 20 daily minutes, so the authorities are just hoping to nudge people in the right direction. It’s like the Dietary Guidelines for Americans advising us to “eat less…candy.” If only they’d just give it to us straight. That’s what I try to do with NutritionFacts.org.

Most of the content in my book How Not to Die came from my video research, but this particular video actually sprung from the book. I wanted to include exercise in my Daily Dozen list, but needed to do this research to see what was the best “serving size.”

I wish someone would start some kind of FitnessFacts.org website to review the exercise literature. I’ve got my brain full with the nutrition stuff—though there’s so much good information I don’t have time to review that there could be ten more sites just covering nutritional science!


For more on all that exercise can do for our bodies and minds, see

Some tips for maximizing the benefits:

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

The Disconnect Between Science and Policy

Back in 1912, when hardly anyone smoked cigarettes, lung cancer was like a museum curiosity: extremely rare. In the next few decades, however, it rose dramatically around the world, roughly fifteen-fold. But researchers had already nailed it way back then. By mid-century, the evidence linking lung cancer and tobacco was considered overwhelming. Says who? Says the tobacco industry’s own research scientists in an internal memo. We now know that “senior scientists and executives within the cigarette industry knew about the cancer risks of smoking at least as early as the 1940s.”

Publically, though, they said things like, “Sure there are statistics associating lung cancer and cigarettes. There are statistics associating lung cancer with divorce, and even with lack of sleep. But no scientist has produced clinical or biological proof that cigarettes cause the diseases they are accused of causing.”

What was the government saying? My video American Medical Association Complicity with Big Tobacco includes several real cigarette advertisements, including one in which a leading U.S. Senator advises readers to smoke Lucky Strikes. Who wouldn’t want to “give [their] throat a vacation,” as another ad proclaimed? Others assured “not one single case of throat irritation,” and how could your throat and nose be adversely affected when cigarettes “are just as pure as the water you drink”? What if you do feel irritation from smoking? No problem—your doctor can write you a prescription for cigarettes, according to an ad from the Journal of the American Medical Association. After all, “don’t smoke” is advice hard for patients to swallow, as we’re told in another ad.

This reminds me of the recent survey of doctors that found the number-one reason doctors don’t prescribe heart-healthy diets was their perception that patients fear being deprived of all the junk they’re eating. After all, Philip Morris reminded doctors in an ad that we want to keep our patients happy and to “make a radical change in habit…may do harm.”

The tobacco industry gave medical journals big bucks to run ads like the ones I’m sharing with you. Should we be concerned about a conflict of interest? Not if we listen to Philip Morris, who assured us their “claims come from completely reliable sources” based on studies conducted by “recognized authorities…whose findings have been published in leading medical journals.” They even kindly offered to send free packs of cigarettes to doctors so they can test them out themselves and invited physicians to “make the doctors’ [smoking] lounge your club” at the American Medical Association convention.

What did the AMA have to say for itself? Like most other medical journals, they accepted tobacco ads but asserted that “[p]ostmortem examinations do not reveal lesions in any number of cases that could be definitely traced to the smoking of cigarettes.” So, as far as the AMA was concerned, case closed.

In fact, even after the Surgeon General’s Report on Smoking and Health came out, the American Medical Association, American Cancer Society, and Congress continued to drag their feet. The government was still subsidizing tobacco, just as our tax dollars subsidize the sugar and meat industries today. The AMA actually went on record refusing to endorse the Surgeon General’s report. Could that have been because they had just been handed ten million dollars from the tobacco industry?

Today the money is coming from big food. The American Academy of Family Physicians has accepted large sums of money from Coca-Cola “to fund patient education on obesity prevention.” I wonder what that pamphlet will say.

Who was featured as a top partner on Coca Cola’s website? The American College of Cardiology.

Just as it would have been hazardous to your health to take the medical profession’s advice on your smoking habits in the 1950s, it may be hazardous to your health today to take the medical profession’s advice on your eating habits.


If the balance of scientific evidence favors plant-based eating, why isn’t the medical profession at the forefront of encouraging people to eat healthier? That’s the question this video tries to answer. Looking back to smoking in the 1950s, we can see how all of society, the government, and even the medical profession itself could be in favor of habits that decades of science had already overwhelmingly condemned as harmful.

For more on the influence industry can have on food policy, 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:

Cancer-Causing Caramel Color

Caramel coloring may be the most widely consumed food coloring in the world.  Unfortunately, its manufacture can sometimes lead to the formation of a carcinogen called methylimidazole, which was identified as a cancer-causing chemical in 2007. For the purposes of its Proposition 65 labeling law, California set a daily limit at 29 micrograms a day. So, how much cancer might caramel-colored soft drinks be causing? We didn’t know…until now… My video Which has more Caramel Coloring Carcinogens: Coke or Pepsi? explores these questions and more.

Researchers tested 110 soft drink samples off store shelves in California and around the New York metropolitan area, including Connecticut and New Jersey. None of the carcinogen was found in Sprite, which is what you’d expect since Sprite isn’t caramel-colored brown. Among sodas that are, the highest levels were found in a Goya brand soda, while the lowest levels were in Coke products, which were about 20 times less than Pepsi products. Interestingly, California Pepsi was significantly less carcinogenic than New York Pepsi. “This supports the notion that [labeling laws like] Proposition 65…can incentivize manufacturers to reduce foodborne chemical risks…” To protect consumers around the rest of the country, federal regulations could be a valuable approach to reducing excess cancer risk—but how much cancer are we talking about?

Johns Hopkins researchers calculated the cancer burden, an estimate of the number of lifetime excess cancer cases associated with the consumption of the various beverages. So, at the average U.S. soda intake, with the average levels of carcinogens found, Pepsi may be causing thousands of cancer cases, especially non-California Pepsi products, which appear to be causing 20 times more cancer than Coke. Of course, there’s no need for any of them to have any these carcinogens at all “as caramel colorings serve only a cosmetic purpose [and] could be omitted from foods and beverages…” But we don’t have to wait for government regulation or corporate social responsibility; we can exercise personal responsibility and just stop drinking soda altogether.

Cutting out soda may reduce our risk of becoming obese and getting diabetes, getting fatty liver disease, suffering hip fractures, developing rheumatoid arthritis, developing chronic kidney disease, and maybe developing gout, as well.

In children, daily soda consumption may increase the odds of asthma five-fold and increase the risk of premature puberty in girls, raising the likelihood they start getting their periods before age 11 by as much as 47 percent.

If we look at the back of people’s eyes, we can measure the caliber of the arteries in their retina, and the narrower they are, the higher the risk of high blood pressure, diabetes, and heart disease. Researchers performed these kinds of measurements on thousands of 12-year-olds and asked them about their soda drinking habits. Their findings? Children who consume soft drinks daily have significantly narrower arteries. “The message to patients can no longer remain the simplistic mantra ‘eat less, exercise more.’” It matters what you eat. “[S]pecific dietary advice should be to significantly reduce the consumption of processed food and added sugar and to eat more whole foods.”


Prop 65 is lambasted by vested interests, but, as I mentioned, it may push manufacturers to make their products less carcinogenic. Other Prop 65 videos include:

For more background on caramel coloring, see my video Is Caramel Color Carcinogenic?.

There are other soda additives that are potentially toxic, too. See my three-part series on phosphates:

Other coloring agents are less than healthy. For more on this, see Artificial Food Colors and ADHD and Seeing Red No. 3: Coloring to Dye For.

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: