It’s well-known that people who are overweight or obese have to work harder than people with a normal weight to perform daily activities like walking, climbing stairs, and carrying groceries. What many don’t know, however, is that this difference in energy expenditure occurs even at rest. A new study looked at why fat people get tired quicker—and found that not only are their bodies unaccustomed to sustained exertion but also that the excess adipose tissue inhibits their ability to expend energy even when sitting still! Here’s what you need to know about this study.

What we’ve been told

• Eat less, exercise more and your body will thank you by shedding excess pounds. But now researchers are coming around to a different conclusion: A significant portion of fat people tire easily because they carry too much fat in their blood. These results suggest that it might be harder for obese individuals to exercise vigorously than lean individuals, says investigator Scott G. Wasserman, MD, medical director of Mayo Clinic’s Weight Management Program and author of an upcoming study in Mayo Clinic Proceedings. So what does it mean if your BMI is on its way to 30?

What the study suggests

• The study suggests that fat people burn less energy because they have slower metabolisms, even when at rest. In contrast, lean people may have a higher metabolic rate because of their higher activity levels and overall muscle mass. Since muscle is much more metabolically active than fat, lean people may be burning more calories than obese individuals at any given moment—even while sitting down. The research team has not yet confirmed whether low-fat diets could help fix metabolic differences between obese and non-obese participants; however, previous studies suggest that it may be possible to increase an individual’s resting metabolism by adding muscle through exercise or strength training.

How this can help you

• Being aware of your diet and taking time to make healthy decisions about what you eat can help you stay fit and energized, even if you're not making drastic changes. That said, it's important to note that eating a balanced diet doesn't necessarily mean eating low-fat foods only; moderate portions of whole grains, fruits, and lean meats are important too. It all comes down to knowing what's good for your body on a physiological level: Some fat (particularly unsaturated fat) is good for your heart health, for example, but too much-saturated fat can lead to clogged arteries. And while some experts believe that consuming lots of sugary foods or refined carbs can be bad for your brain, others disagree — which is why a study like this one is so helpful.

What you can do about it

• While we're on such a roll with studies, let's talk about another one. This new study also investigated chronic fatigue in fat people, but instead of focusing on physical activity levels, it looked at perceived energy levels and found that fat people are more likely to feel tired. So does that mean fatness causes exhaustion? Well, not exactly—it could be an issue of body image and self-esteem. When you feel bad about your body, it may be harder to take care of yourself (for example, eating healthfully or exercising regularly) or to see your weight as something that can be changed through hard work rather than simply accepted as who you are.

The final word (another way)

• Do you think carbohydrates are unhealthy? You may be surprised to learn that carbohydrates provide a necessary source of energy for our bodies. That said, however, there’s no disputing that excessive carbohydrate consumption can lead to weight gain. Recent research has confirmed what many suspected all along: consuming too many refined carbohydrates is likely one of the leading culprits behind obesity rates in developed countries like Canada and the U.S. As such if you’re trying to lose weight by reducing your intake of refined carbs—including sugar-sweetened beverages like soda—you might also want to reduce your overall calorie intake by skipping heavy foods with cream sauces and other added fats.

Final thoughts

• The short answer is, yes, fat people do get tired quicker, and for good reason. The story behind your question is that when we look at studies on metabolism in obese vs. lean individuals, we see changes in how their bodies utilize energy. Specifically, researchers noted differences in resting energy expenditure (REE), or how much energy they expend while sitting around doing nothing as well as sleeping metabolic rate (SMR), or how much energy they burn while sleeping. Studies have found that obese individuals tend to have a lower REE compared to lean counterparts it’s been shown that 35% of the weight-related variation in REE can be attributed to body mass index.