Technically, most people (other than bodybuilders and athletes) are at a healthy bodyweight when their body mass index (BMI) is between 18.5 and 25 kg/m^2. BMI is simply the ratio between your bodyweight and height squared using the metric system of calculation. As simple as the calculation is, BMI does have a significant drawback since body composition is not taken into consideration. For those people who have more lean body mass (muscle) than the average person, BMI will be higher. For example, bodybuilders and athletes tend to have BMI's that put them in the overweight category (BMI > 25 kg/m^2). Thus, despite being "overweight", bodybuilders and athletes are actually lean (i.e., low bodyfat) since much of their bodyweight is attributed to muscle mass. Despite its limitation, BMI is still a good parameter to use in practice since most people are not bodybuilders or athletes.
Being underweight means having a BMI less than 18.5 kg/m^2. The health risks of being underweight are the following:
- osteoporosis (higher risk of bone fracture)
- reduced ability of the body to regulate its temperature
Being overweight means having a BMI greater than 25 kg/m^2. The health risks of being overweight are the following:
- type-2 diabetes (increased insulin resistance)
- hypertension (elevated blood pressure more than 130/85 mm Hg)
- heart disease (increased LDL, triglyceride and total cholesterol level, decreased HDL)
- sleep apnea
- certain cancers (increased estrogen level)
- gallbladder disease
If you are underweight, you should eat more nutrient- and energy-dense foods that contain relatively high amounts of micronutrients (i.e., vitamins and minerals) and are also relatively high in calories per gram. Essentially this means eating foods that contain less water, are lower in fiber, and have a higher fat content. A gradual increase in caloric intake (i.e., 250 kcals/day) is recommended. Increase juice and milk consumption, choose foods that are not low-fat as well as less complex-carb products, eat larger portion sizes, perform physical activity (i.e., no more than 60 minutes daily), increase the number of meals consumed, and decrease protein intake to lessen satiety.
If you are overweight, you should eat less energy-dense foods having more water, are higher in fiber, and have a lower fat content. A gradual decrease in caloric intake (i.e., 500 kcals/day) is recommended. Eat plenty of fruits and vegetables, increase water consumption, choose low-fat as well as complex-carb products, avoid empty-calorie foods which contain a lot of sugar, eat smaller portion sizes, eat slowly, increase physical activity level (i.e., at least 60 minutes daily), increase the number of meals consumed, and increase protein intake to promote satiety.
Brian Danley, CFT
"Motivation is what gets you started. Habit is what keeps you going."