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:

What Happens if You Have Red Wine or Avocados with a Meal?

Whole plant sources of sugar and fat can ameliorate some of the postprandial (after meal) inflammation caused by the consumption of refined carbohydrates and meat.

Studies have shown how adding even steamed skinless chicken breast can exacerbate the insulin spike from white rice, but fish may be worse. At 0:18 in my video The Effects of Avocados and Red Wine on Meal-Induced Inflammation, you can see how the insulin scores of a low-carbohydrate plant food, peanuts, is lower compared to common low-carb animal foods—eggs, cheese, and beef. Fish was even worse, with an insulin score closer to doughnut territory.

At 0:36 in my video, you can see the insulin spike when people are fed mashed white potatoes. What do you think happens when they’re also given tuna fish? Twice the insulin spike. The same is seen with white flour spaghetti versus white flour spaghetti with meat. The addition of animal protein may make the pancreas work twice as hard.

You can do it with straight sugar water, too. If you perform a glucose challenge to test for diabetes, drinking a certain amount of sugar, at 1:10 in my video, you can see the kind of spike in insulin you get. But, if you take in the exact same amount of sugar but with some meat added, you get a higher spike. And, as you can see at 1:25 in my video, the more meat you add, the worse it gets. Just adding a little meat to carbs doesn’t seem to do much, but once you get up to around a third of a chicken’s breast worth, you can elicit a significantly increased surge of insulin.

So, a chicken sandwich may aggravate the metabolic harm of the refined carb white bread it’s on, but what about a PB&J? At 1:49 in my video, you can see that adding nuts to Wonder Bread actually calms the insulin and blood sugar response. What if, instead of nuts, you smeared on an all fruit strawberry jam? Berries, which have even more antioxidants than nuts, can squelch the oxidation of cholesterol in response to a typical American breakfast and even reduce the amount of fat in your blood after the meal. And, with less oxidation, there is less inflammation when berries are added to a meal.

So, a whole plant food source of sugar can decrease inflammation in response to an “inflammatory stressor” meal, but what about a whole plant food source of fat? As you can see at 2:38 in my video, within hours of eating a burger topped with half an avocado, the level of an inflammatory biomarker goes up in your blood, but not as high as eating the burger without the avocado. This may be because all whole plant foods contain antioxidants, which decrease inflammation, and also contain fiber, which is one reason even high fat whole plant foods like nuts can lower cholesterol. And, the same could be said for avocados. At 3:12 in my video, you can see avocado causing a significant drop in cholesterol levels, especially in those with high cholesterol, with even a drop in triglycerides.

If eating berries with a meal decreases inflammation, what about drinking berries? Sipping wine with your white bread significantly blunts the blood sugar spike from the bread, but the alcohol increases the fat in the blood by about the same amount. As you can see at 3:40 in my video, you’ll get a triglycerides bump when you eat some cheese and crackers, but if you sip some wine with the same snack, triglycerides shoot through the roof. How do we know it was the alcohol? Because if you use dealcoholized red wine, the same wine but with the alcohol removed, you don’t get the same reaction. This has been shown in about a half dozen other studies, along with an increase in inflammatory markers. So, the dealcoholized red wine helps in some ways but not others.

A similar paradoxical effect was found with exercise. If people cycle at high intensity for about an hour a half-day before drinking a milkshake, the triglycerides response is less than without the prior exercise, yet the inflammatory response to the meal appeared worse, as you can see at 4:18 in my video. The bottom line is not to avoid exercise but to avoid milkshakes.

The healthiest approach is a whole food, plant-based diet, but there are “promising pharmacologic approaches to the normalization” of high blood sugars and fat by taking medications. “However, resorting to drug therapy for an epidemic caused by a maladaptive diet is less rational than simply realigning our eating habits with our physiological needs.”

Protein from meat can cause more of an insulin spike than pure table sugar. See the comparisons in my video Paleo Diets May Negate Benefits of Exercise.

Interested in more information on the almond butter study I mentioned? I discuss it further in How to Prevent Blood Sugar and Triglyceride Spikes After Meals.

Berries have their own sugar, so how can eating berries lower the blood sugar spike after a meal? Find out in If Fructose Is Bad, What About Fruit?


For more on avocados, check out:

And here are more videos on red wine:

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:

Are the BPA-Free Plastics Like Tritan Safe?

Do BPA-free plastics such as Tritan, have human hormone-disrupting effects? And what about BPS and BPF?

Recent human studies indicate that exposure to the plastics chemical BPA may be associated with infertility, miscarriage, premature delivery, reduced male sexual function, polycystic ovaries, altered thyroid and immune function, diabetes, heart disease, and more. Yet, “[a]s recently as March 2012, FDA stated that low levels of BPA in food are considered safe.” However, just months later, to its credit, the agency banned the use of BPA plastics in baby bottles and sippy cups. Regulators standing up to industry? Maybe I shouldn’t be so cynical! But, wait. The ban was at the behest of the plastics industry. It had already stopped using BPA in baby bottles so it was their idea to ban it.

The industry had switched from BPA to similar compounds like BPF and BPS. So, our diets now contain everything from BPA to BPZ, and the majority of us have these new chemicals in our bodies as well. Are they any safer?

As I discuss in my video Are the BPA-Free Alternatives Safe?, based on the similarities of their chemical structures, they are all predicted to affect testosterone production and estrogen receptor activity, as you can see at 1:40 in my video. However, they were only recently put to the test.

As you can see at 1:50 in my video, we’ve known BPA significantly suppresses testosterone production, and, from “the first report describing BPS and BPF adverse effects on physiologic function in humans,” we know those compounds do, too. Well, kind of. The experiments were performed on the testicles of aborted human fetuses. But, the bottom line is that BPS and BPF seem to have “antiandrogenic anti-male hormone effects that are similar to those of BPA.” So when you’re assured you shouldn’t worry because your sales slip is BPA-free, the thermal paper may just contain BPS instead. What’s more, BPS receipts may contain up to 40 percent more BPS than they would have contained BPA. So BPA-free could be even worse. In fact, all BPA-replacement products tested to date released “chemicals having reliably detectable EA,” estrogenic activity.

This includes Tritan, which is specifically marketed as being estrogen-activity-free. As you can see at 3:06 in my video, however, researchers dripped an extract of Tritan on human breast cancer cells in a petri dish, and it accelerated their growth. This estrogenic effect was successfully abolished by an estrogen blocker, reinforcing it was an estrogen effect. Now, the accelerated growth of the cancer cells from the Tritan extract occurred after the plastic was exposed to the stressed state of simulated sunlight. Only one out of three Tritan products showed estrogen activity in an unstressed state, for instance when they weren’t exposed to microwaving, heat, or UV rays. “Because there would be no value in trading one health hazard for another, we should urgently focus on the human health risk assessment of BPA substitutes.”

In the meanwhile, there are steps we can take to limit our exposure. We can reduce our use of polycarbonate plastics, which are usually labeled with recycle codes three or seven, and we can opt for fresh and frozen foods over canned goods, especially when it comes to tuna and condensed soups. Canned fruit consumption doesn’t seem to matter, but weekly canned vegetable consumption has been associated with increased BPA exposure. If you do use plastics, don’t microwave them, put them in the dishwasher, leave them in the sun or a hot car, or use once they’re scratched. But using glass, ceramic, or stainless steel containers is probably best.


For more on BPA, check out my videos:

Unfortunately, BPA isn’t the only plastics chemical that may have adverse health effects. 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: