Metabolically Healthy Obesity | Endocrine Reviews | Oxford Academic 

This isn’t to say that weight management shouldn’t be a priority for someone with obesity, regardless of whether or not they’re healthy. BMI is still a strong predictor of disease risk. But it is a clear reminder that weight isn’t the sole barometer of health.

What makes people with metabolically healthy obesity different from those who are less healthy isn’t quite clear. If two people have the same BMI and the same amount of body fat, what’s making one of them healthier than the other? 
 

It might have something to do with the unique characteristics of their fat tissue.
 

All fat is not created equal

Gaining and losing weight requires an energy surplus and energy deficit, respectively. When we're in energy balance, our weight stays the same. But even in the absence of weight loss, consuming a healthy diet and exercising could change the composition of our fat tissue on a cellular level to make it healthier. For example, healthier fat tissue may be more metabolically active, produce less inflammatory cytokines, and be composed of less fibrotic tissue.

There’s one more characteristic of healthy fat tissue that might promote system-wide health benefits: it has a greater capacity to store lipids and fatty acids. Metabolic dysfunction worsen our body’s ability to store lipids. Rather than sit in our fat cells, these lipids circulate throughout the body where they can accumulate around our organs and muscles, contributing to insulin resistance and inflammation—two root causes of chronic disease. If there were a way to increase the lipid-storage-capacity of our fat, it would have some major health benefits.

Even though the effects of exercise on weight loss are modest at best—especially long-term—it’s still recommended to people with overweight or obesity. Of course, exercise can help with weight loss in these people when combined with other lifestyle interventions like dieting. And even without losing any weight, exercise makes people healthier by improving risk factors like blood pressure, blood glucose, and blood lipids.
 

What if there was another way that exercise was improving our healthspan? A route not by which it melted the fat off of our body, but by which it made the fat that we do have healthier?
 

That was the finding of a recent study published in Nature Metabolism.

Same BMI, different bodies

Researchers were interested in whether characteristics of fat tissue would be different between self-reported regular exercisers and non-exercisers. To investigate this, they recruited a total of 32 adults with overweight or obesity (their average BMI was ~30)—16 of whom had participated in endurance exercise for a minimum of a few years and 16 of whom did not exercise regularly. Both groups were matched for BMI and had the the same body fat percentage.

Not only did the regular exercisers have a 25% higher VO₂ max and better indices of cardiometabolic health across the board (e.g., insulin sensitivity), but they also had profoundly healthier fat tissue.
 

Analyzing abdominal subcutaneous adipose (fat) tissue (aSAT) samples from the exercisers revealed some incredible differences compared to the sedentary participants. The fat from the regular exercisers had:

• A more favorable extracellular matrix composition
• Fewer inflammatory macrophages
• More mitochondria
• A greater fat-storage. capacity

While the size of fat cells was nearly identical between the two groups, the exercised fat cells were more dense with capillaries, allowing more oxygen and nutrient delivery to their tissues. When fat cells from the exercisers were subjected to meticulous ex vivo experiments, they also displayed a greater capacity for angiogenesis—the body’s process of creating new blood vessels. When placed into a special growth medium, exercised fat tissue sprouted more capillaries.
 

Along with having fat cells more dense in capillaries, the regular exercisers had fat cells with a better lipid-storage capacity. Their fat cells were also more enriched with mitochondrial proteins, likely a direct result of the effects of prolonged endurance exercise training, which is a potent enhancer of mitochondrial biogenesis.
 

Several of these characteristics of fat tissue from exercisers and non-exercisers may boil down to one fundamental difference—a greater capacity for protein translation in exercised fat tissue. 

Protein translation is our body’s way of making new proteins in response to stress or metabolic demands, allowing it to adapt and grow stronger to withstand the next stressor. Protein translation is what allows us to adapt to heat by using the sauna, cold by using deliberate cold exposure, and cellular energetic stress by fasting or engaging in vigorous exercise. The fat tissue from people with years of endurance exercise training was better at responding and adapting to stress by upregulating protein synthesis, a process controlled by ribosomes.

Long-term exercise training has positive effects on adipose tissue in overweight or obesity | Nature Metabolism 

Causation or correlation?

We’re still left with a major unknown.
 

According to nearly any measure, the exercisers in this study were healthier. They had lower levels of insulin and glucose, better insulin resistance, and higher HDL cholesterol. Can we conclude that their superior cardiometabolic health is caused by their healthier fat tissue characteristics? 

It’s hard to say.
 

We know that having an abundance of fat circulating in the blood is not a good thing. Fatty acids can end up in storage depots around the heart, liver, and skeletal muscle (as triacylglycerols) where they promote insulin resistance—the primary culprit in nearly all cardiometabolic diseases including obesity and diabetes. Inflammation is also higher in many disease states and contributes to poor health in people with excess adiposity. If exercise turns fat tissue into a reservoir for storing lipids and quells its proinflammatory potential this would in turn lead to better metabolic health.

A question I'm very interested in and will have to wait to find out is whether "metabolically healthy obese" people have similar indices of cardiometabolic health and fat tissue characteristics compared to normal-weight exercisers and non-exercisers!
 

All of this should be welcome news to everyone. For people who are trying to lose weight and using exercise to accomplish their goal, there may be a dual benefit to breaking a sweat: less fat and healthier fat.
 

For people who aren’t trying to lose weight, exercise is turning your fat healthier with every step taken, even if you don’t shed a single pound.
 

And for people who might have experienced some weight gain for whatever reason—be it aging, pregnancy, injury or the holidays—these data reinforce the fact that sustaining a physically active lifestyle might lessen the burden of extra adiposity. Exercise has so many health benefits independent of its effect on weight—let’s embrace that.

Thanks for reading.

If you want to learn more about how exercise can make fat tissue healthier, even without weight loss, you can watch two of my Question & Answer episodes, #33 and #44.

Relevant weight loss timestamps:

• 1:02:13 - Is counting calories or carbohydrates better for losing weight?
• 1:03:12 - Are carbohydrates the problem or is it refined carbohydrates that are the real issue?
• 1:04:40 - Why low-carb and paleo diets became so popular
• 1:05:30 - How energy balance dictates whether we gain or lose weight
• 1:06:02 - Highly processed foods lead people to eat more calories overall
• 1:06:30 - Why carbohydrates from healthy whole foods like fruit are beneficial
• 1:07:19 - Should you avoid store-bought fruit smoothies and juices?
• 1:07:41 - Is sourdough bread healthy?

Relevant exercise timestamps:

• 00:01:37 - The benefits of exercise in cardio zones 2 and 5 or heath and longevity
• 00:02:26 - How zone 2 training is defined
• 00:03:50 - Is zone 2 training beneficial for weight and fat los?
• 00:04:20 - How much zone 2 training you should engage in per week for longevity
• 00:05:18 - What are the current recommendations for moderate-to-vigorous exercise?
• 00:05:45 - Rhonda's exercise routine
• 00:30:04 - Does berberine inhibit the beneficial effects of exercise?