There's no single answer to the question posed by the title that is right for everyone, of course. There are a variety of natural body types, some very thin, others on the stocky side. Still, official sources state that people now consume about 22% more calories daily than they did a generation ago. In light of that, it shouldn't be surprising that society is tending toward obesity today.

A good exercise program is one of the twin pillars that can help reverse that trend. Along with the increased consumption has come a decrease in the amount of exercise the average person gets today. More time at the computer and a host of other reasons are responsible.

But the right diet is the other pillar that is a must. A 'must', that is, if the goal is optimal weight and body fat percentage, an attractive appearance, self-esteem and overall health. It isn't mere vanity that prompts millions to seek that diet. They know, most having tried to diet at one time or another, that many real benefits follow.

Dieting is about more than just losing weight. It's just as much about achieving optimal nutrition. It's about creating the body image that you feel comfortable with. It's about achieving your unique optimal weight range.

Note that important phrase 'weight range'. No exact number represents your ideal weight. It will fluctuate slightly from week to week. What that range is depends on your BMI (Body Mass Index), your waistline and where you store fat, your natural body type and other factors.

BMI is just your weight (in kilograms) divided by your height (in meters) squared, or BMI = Weight / (Height x Height). To find your weight in metric units, just divide by 2.2, to find your height in meters, multiply inches by 2.54 and divide by 100.

So, suppose you are a woman 5 feet 6 inches tall, weighing 140 lbs. So, (66 inches x 2.54)/100 = 1.676 meters. Your Weight = 140 / 2.2 = 63.6 kg. Therefore, your BMI = 63.6 / (1.676 x 1.676) = 22.6, which is right in the middle of the normal range. See the full table and a BMI calculator here: http://www.consumer.gov/weightloss/bmi.htm

But a woman 5 feet 6 inches who weighs a 140 pounds may still feel the need to diet. It's not then strictly just a health issue. She may want to feel more attractive. She may legitimately believe that a slimmer physique or one with more muscle will give her more energy.

Or, she may not. That's where self-image plays a significant role. She may adjust her body, or her attitude, or both. Or, she may be perfectly satisfied with herself as she is.

Part of that outlook will (and should) depend on age and personal circumstances. If that same woman is 26 she may feel the need to shed a few pounds in order to achieve her personal goal. If she's 16, she likely has a few years of growth left and the whole situation will sort itself out with time. If she's 56, she might be very pleased that she is in a healthy range and not pay much heed to other factors, but still want to diet to achieve optimal nutrition.

Personal situations count heavily when deciding whether or not to diet.