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 Foods With the Highest Aspirin Content

The results of a recent aspirin meta-analyses suggesting a reduction of cancer mortality by about one-third in subjects taking daily low-dose aspirin “can justly be called astounding.” Yet the protection from “Western” cancers enjoyed by those eating more traditional plant-centered diets, such as the Japanese, “is even more dramatic.” I examine this in my video Plants with Aspirin Aspirations.

Before the Westernization of their diets, animal products made up only about 5 percent or less of the Japanese diet. At 0:37 in my video, you can see the difference in cancer mortality of U.S. men and women compared with Japanese men and women. “[A]ge-adjusted death rates from cancers of the colon, prostate, breast, and ovary were on the order of 5–10-fold lower in Japan than in the US at that time; mortality from pancreatic cancer, leukemias, and lymphomas was 3–4-fold lower in Japan. But this phenomenon was by no means isolated to Japan; Western cancers were likewise comparatively rare in other societies where “people ate plant-based diets.”

“The cancer protection afforded by lifelong consumption of a plant-based diet, in conjunction with leanness and insulin sensitivity (which tend to be promoted by low-fat plant-based diets)…may be very substantial indeed.” Therefore, a “lifestyle protocol for minimizing cancer risk” may include a whole-food plant-based diet.

If part of this cancer protection arises out of the aspirin phytonutrients in plants, are there any plants in particular that are packed with salicylates? Though salicylic acid, the main active ingredient in aspirin, is “ubiquitously present in fruits and vegetables,” the highest concentrations are found in herbs and spices.

Red chili powder, paprika, and turmeric contain a lot of salicylates, but cumin is about 1 percent aspirin by weight. Eating a teaspoon of cumin is like taking a baby aspirin. (See the table at 1:54 in my video for details on other herbs and spices, and their salicylate content.) “Consequently, populations that incorporate substantial amounts of spices in foods may have markedly higher daily intakes of salicylates. Indeed, it has been suggested that the low incidence of colorectal cancer among Indian populations may be ascribed in part to high exposure to dietary salicylates throughout life from spice consumption.”

“The population of rural India, with an incidence of colorectal cancer which is one of the lowest in the world, has a diet that could be extremely rich in salicylic acid. It contains substantial amounts of fruits, vegetables, and cereals flavored with large quantities of herbs and spices.” Some have proposed it’s the curcumin in the spice turmeric (which I discuss in detail in my video Turmeric Curcumin and Colon Cancer), but it may be the salicylic acid in cumin—and the spicier the better.

A spicy vegetable vindaloo may have four times the salicylates of a milder Madras-style veggie dish. As you can see from the chart at 2:55 in my video, after just one meal, we get an aspirin spike in our bloodstream like we just took an aspirin. So, eating flavor-filled vegetarian meals, with herbs and spices, may be more chemoprotective—that is, more protective against cancer—than regular, blander vegetarian meals.

We may also want to eat organic produce. “Because salicylic acid is a defense hormone of plants, the concentration…is increased when plants become stressed,” like when they are bitten by bugs (unlike pesticide-laden plants). Indeed, soups made from organic vegetables were found to have nearly six times more salicylic acid than soups prepared from conventionally grown ingredients.

We should also choose whole foods. Whole-grain breads, which are high in salicylic acid, contain about 100 times more phytochemicals than white bread: 800 phytochemicals compared to 8.

“Interest in the potential beneficial effects of dietary salicylates has arisen, in part, because of the extensive literature on the disease-preventative effects of Aspirin™. However, it should not be forgotten that plant products found to contain salicylic acid are generally rich sources of other phenolic acids…[and many] also have a marked anti-inflammatory and redox-related bioactivity [that is, antioxidant activity] in mammalian cells. Their potential protective effects should not be overlooked. In this context, the importance of dietary salicylic acid should not perhaps be over emphasised…Indeed, some believe that ‘salicylic acid deficiency’ has important public health implications and that it should be classed as an essential vitamin, namely ‘Vitamin S’.”

What they’re saying is that we should all eat a lot of plants.


If you missed the first two videos in this series, see Should We All Take Aspirin to Prevent Heart Disease? and Should We All Take Aspirin to Prevent Cancer?.

The drug-like anti-inflammatory power of certain plant foods may make them a risky proposition during pregnancy. See Caution: Anti-Inflammatory Foods in the Third Trimester.

Herbs and spices not only have some of the most anti-inflammatory properties, but they also are well-rounded protectants. 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 presentations: