How Much Is Too Much?

What diet best supports our physical fitness? I was shocked to learn that endurance athletes had more atherosclerosis than sedentary people. At see.nf/athletes you can see a review of the research. They don’t overtax their hearts with exercise, but with food. Endurance athletes sometimes consume 5000, 6000, or even 7000 calories a day. So if they’re taking in twice as much saturated fat and cholesterol, it’s no wonder that it really takes a toll on the heart.

What do you think happened when a research team prescribed participants a Paleo diet and high-intensity circuit training along CrossFit lines? Normally, it hardly matters how you lose weight—through exercise, a gastric band, or tuberculosis—cholesterol levels drop for a while no matter what you eat. After ten weeks of intensive exercise and weight loss thanks to a Paleo diet, however, the participants’ LDL cholesterol level increased. It doesn’t seem to be enough to offset this risk by changes in the amount of LDL cholesterol or HDL cholesterol. And those who were healthiest at the start recorded the worst increase. In participants with originally optimal LDL levels (under 70), this greatest risk factor for heart disease, our number one killer, rose by 20 percent. Exercise is supposed to improve things, not make them worse.

On the other hand, the level of bad cholesterol in participants who ate a plant-based diet and went for walks fell by 20 percent after three weeks, whereas the Paleo diet “nullified the beneficial effects of exercise.” That’s why all athletes should eat more plant-based. If you’re dead, you can’t exercise anymore.

Plant Power

The number of athletes interested in a plant-based diet has risen rapidly, due in part to documentaries like The Game Changers. (I had the honor of playing a small role in that film as a scientific adviser.) There is a general desire not only to do something good for one’s long-term health, but also to improve performance and shorten recovery times. The artery-dilating, antioxidant, and anti-inflammatory properties of a plant-based diet lead to improved circulation, lower oxidative stress, and less inflammation, and it has been found that cardiovascular and respiratory fitness in athletes is indeed better and that they have greater endurance, perhaps because of their improved heart function. (See see.nf/fitness for a quick overview of the studies.) However, the more important question from the perspective of general health is how diet affects fitness in training programs in people who are not athletes.

People with type 2 diabetes took part in a randomized trial in which both groups ate calorie-reduced diets, but one ate vegetarian and the other conventional, and both exercised. All meals were provided so that everyone adhered to the prescriptions, and the exercise program was strictly monitored. Although everyone moved the same amount, VO2max (a measure of aerobic fitness) rose by 12 percent in the vegetarian group, and maximal performance increased by 21 percent, both significantly better than in the nonvegetarian group, in which no clear improvements were seen in either area. In other words, the results suggested that a more plant-based diet improves fitness more efficiently—both aerobic capacity and strength—than a less plant-based diet with the same aerobic exercise program.

The meat-free group also felt less depressed and noted an improvement in their quality of life and mood. This is consistent with randomized crossover studies showing that when saturated fat intake is increased in participants without their knowledge, it can bring about reversible deteriorations in brain function, inflammation markers, mood, and resting metabolic rate, and may even undermine motivation to exercise. Study participants who ate a lot of saturated fat were between 12 and 15 percent less physically active than others who ate only small amounts.

Compared with the group on the conventional calorie-controlled diet, the vegetarian group had improved values for body weight, blood sugar, cholesterol, insulin sensitivity, and oxidative stress. The two diets contained the same number of calories, but simply avoiding meat led to about three kilograms more weight loss in the vegetarian group; in addition, participants ended up with a significantly slimmer waist, their flabby subcutaneous fat decreased, and most importantly, they lost significantly more visceral fat, the most metabolically dangerous fat in the abdominal cavity. And all of that on top of improved conditioning.

Weight Regulation

Over the past 40 years, the number of people with obesity among older adults has tripled. 43 percent of Americans over 60 are not only overweight but obese. You can’t chalk that up solely to a slower metabolism. Our resting metabolic rate (the calories we burn to stay alive) stays the same between 20 and 60 and then drops by only about ten daily calories each year after that. So don’t point the finger at your metabolism. As I documented in detail in my book How Not to Diet, you have to point to your food.

Obesity is associated with accelerated cellular aging, meaning telomere shortening or advanced epigenetic age, presumably through the oxidative stress and systemic inflammation that accompany excess body fat. Obesity means declining physical function, that is, limited mobility, and declining cognitive function. MRI scans of hundreds of people in all age groups showed that the white matter of overweight and obese people had shrunk to the extent that the people appeared ten years older. A meta-analysis of 19 studies that had followed more than half a million people for up to 42 years found that obesity in midlife carried a 33 percent higher risk of dementia and that from age 50 onward, every BMI point greater than 20 brought forward the onset of Alzheimer’s by seven months. How does obesity relate to mortality?

Going with Your Gut

The obesity epidemic is partly responsible for the fact that in America we are raising a generation that will live less long than their parents. This downward trend in life span will likely accelerate further as today’s younger generation, which already weighed more earlier, reaches adulthood. According to some projections, in the coming decades we in the United States will lose between two and five years of our life expectancy, perhaps even more. To put that in perspective: a miracle drug that could cure all cancers would add only three and a half years to the average American life span. In other words, if we reverse the obesity epidemic, we will save more lives than by curing cancer.

Even if someone gains only a little weight in midlife, about five to ten kilograms, their odds of later healthy survival drop noticeably. In a study of more than 600 centenarians, fewer than 2 percent of the women and not a single man was obese. Starting at age 40, obesity can shorten life expectancy by as much as six or seven years.