I've been asked this quite a few times, so thought this was right to post this!
The Short Answer:
There are always anomalies, but generally, the answer is no. The laundry list of ailments that accompany excess body fat grows every day: type 2 diabetes, high blood pressure, cancer, osteoarthritis, sleep apnea, and on and on.
Mind you, I'm not talking about a few extra pounds. You can be healthy as a horse without a six-pack or that little gap skinny women have between their thighs when they wear boy shorts. If you eat a nutritious, varied diet and exercise regularly, you may not be as thin as the bikini model who lives across the street, but you're fine. Healthy comes in all shapes and sizes—except maybe XXXL.
The Long Answer:
Before considering the science, consider the common sense. Being overweight or obese means you're lugging extra pounds around. If it's just a matter of five or six lbs. over your ideal weight, then it's not that big of a deal. It's kind of like spending all your time with a backpack filled with textbooks. But once you go beyond that, you're putting a lot of strain on your body. Imagine carrying around a 50-lb. dumbbell all day, every day. It's almost as though you're forcing your body into a perpetual state of overtraining. That extra weight puts pressure on your joints, which can lead to arthritis. It also puts extra pressure on your cardiovascular system, which can lead to heart complications.
Then, there's the question of diet. Overweight people tend to eat too many calories—and those calories are often heavy on the refined carbs and "bad" fats. Both of these substances can cause a buildup of plaque on arteries. Refined carbs can also cause insulin resistance, leading to type 2 diabetes.
There are also the other illnesses that, according to the National Institute of Health
, are statistically higher in heavier people, including colon, breast, endometrial, and gallbladder cancers, sleep apnea, and gallstones.
Much of the media glossed over the fact that the JAMA study made a distinction between "obese" and "overweight." Overweight people with a body mass index (BMI) between 25 and 29 were the ones who supposedly lived longer. "Grade 1" obese people with a BMI between 30 and 34 fared the same as normal-weight people. People with a BMI of 35 or more had the highest risk of death of anyone.
Unfortunately (for overweight people), the review turned out to be flawed and spent the rest of 2013 being roundly criticized. The Center for Science in the Public Interest reported on a number of flaws in their newsletter Nutrition Action. The study didn't account for smokers, who tend to be thinner. It didn't account for people with cancer, dementia, or emphysema; all who tend to lose weight. It also didn't account for age, and people tend to lose weight before they die of old age–related illnesses. So people can become thin—too thin—when they're sick or dying, but that doesn't mean being thin was the cause of death. Not accounting for this threw off the numbers.
Next, the Canadians jumped into the fray, releasing their own meta-review that accounted for people with metabolic syndrome
—a group of conditions that includes high blood pressure, high blood sugar levels, dodgy cholesterol, and excess abdominal fat. These put you at higher risk for heart disease and diabetes. They found that metabolically unhealthy people were at risk regardless of weight. However, when they looked at people without metabolic issues, they found that obese ones had a higher risk of death.
Healthy overweight and healthy normal-sized people had the same level of risk. However, overweight people had slightly higher metabolic markers (for instance, slightly higher blood pressure) and this indicated a greater chance of complications down the road.
To sum all this up, if you're obese, you should really do something about it because multiple studies have confirmed that you're more susceptible to the shopping list of sicknesses listed above. But if you're just a little overweight, you may or may not be in trouble; it depends on who you want to believe.
Or take me. I'm 5' 11", 160 pounds. My BMI is 23, which puts me right in the middle of "normal." However, I also have about 9% body fat, which is considerably below "normal." According to the American Council on Exercise, 14–17% is a "fitness" level and 18–24% is "normal." If I'd added that amount of fat to my frame, my BMI would classify me as overweight, maybe even obese.
So you need to take all this science with a grain of salt.
If your BMI is 30+, your waistline is on or near to 35 inches (for women) or 40 inches (for men), and you don't know a barbell from a kettlebell, then you're probably obese and headed for trouble. Otherwise, use your common sense as a guide.
Does your blood work come back sparkling? Do you eat a diet that's primarily veggies and fruits, followed by whole grains, lean proteins, and good fats? Do you eat little or no added sugar, processed food, and fried food? Do you work out or get some serious exercise at least 4 times a week? Do you feel good in your body? If you can answer "yes" to these things, you're probably at a good weight—and if you're not, you'll get there soon enough.