And some of those fad diets might make you really sick.
It's not just pop-up ads and infomercials that tell us we need to lose weight, doctors have been prescribing weight loss for years as a treatment for a multitude of symptoms and illnesses. Which is disconcerting when 97% of people who lose significant weight through dieting gain it back within five years. Dieting, independent of genetics, is actually likely to cause weight gain over time, not loss. And as a treatment it doesn't make much sense either, since weight loss doesn't blood pressure, fasting glucose, or triglyceride levels for most people (which are stronger indicators for overall health than the number on the scale). The evidence that weight loss is beneficial to your health is sketchy at best, but the evidence that it's actually more likely to make you sick is much stronger.
How sick are we talking?
Diet, exercise, and weight-loss medication don't work, and "yo-yo dieting is linked to heart disease, insulin resistance, higher blood pressure, inflammation, and, ironically, long-term weight gain" (via). Deprivation diets and intense exercise regimens will slim your body in the short-term. They can also cause dehydration, shortness of breath, drops in blood pressure, and heart palpitations, and that's not including long-term problems like a slowed down metabolism, damaged blood vessels, and cardiac stress. Repeat crash diets can also increase your risk for heart attacks (via). And don't forget psychological effects! Immediate side effects are anxiety, irritability, dizziness, cold intolerance, decreased sex drive, difficulty concentrating, muscle soreness, hair loss, and decrease in coordination. Later effects include obsessive tendencies, and in some cases severe psychological stress including suicide attempts and self-mutilation (via). None of that sounds healthy to me.
The "obesity paradox".
Data is suggesting that for some illnesses, a higher BMI is actually a predictor of better health, not the reverse. In one long-term (ten year) study, the prognosis of 'underweight' patients with type 2 diabetes was actually the worst, and those who were 'overweight' lived longer (via). Similar results were found in a study of heart-related deaths. The reason these results might be so baffling is because the BMI is a terrible indicator of health. It doesn't measure bone density, it doesn't differentiate between different types of tissue, and it can't measure things like diet and activity. All it can do is measure the relationship between your weight and your height.
What can you really do to stay healthy?
Don't smoke, and cut down on alcohol. Get moderate exercise a few times a week. Get five servings of fruits and veggies every day. Those are the lifestyle habits of people who are healthy- and that is true of people who are fat AND thin. When it comes to long-term health and life expectancy those habits are consistent. Not restrictive diets. Not burning more calories than you consume in deadly workouts.