One of the ways that we normally judge how healthy we are, is by looking at our body weight. A strong muscular figure for men, and the curvy model-like figure for women are the looks to die for these days. But are we pushing ourselves to unrealistic expectations? What really is a healthy weight? This answer is not a one-size-fits-all. A person is considered to have a healthy weight when his or her weight is:

  • achievable without constantly having to be on a diet
  • compatible with homeostasis in the body i.e. all vital signs are normal (blood pressure, lipid and glucose levels, heart rate, respiratory rate and body temperature)
  • is consistent with good eating habits and regular physical activity 

The body mass index (BMI) is used as an index to determine healthy weight. As shown in the chart below, it tells you if your height to weight ratio puts you in the category of underweight, healthy weight, overweight or obese.

BMI chart.svg
Source: wiki chart

The BMI is calculated by dividing weight by height i.e.

BMI = (kg/m2) = weight (kg/height (m2), or 

BMI = (kg/m2) = [weight (lb/height (inches2)] X 703

Using body mass as your measure of a healthful weight comes with some limitations. It is calibrated for younger people. Therefore if you are over 65, it may not be a good tool for you. Of course, if you are pregnant it’s not going to work either. During this time your BMI will be higher than normal but this does not mean you are overweight. The same can be applied to athletes like football players who have a huge muscular upper body. Their BMI would indicate they are overweight, but as we know this is not at all correct.

Measurements of actual fat composition are more helpful when BMI comes up short e.g. hydrostatic weighing , bod pod, skinfold test, bioelectrical impedance and dual-energy X-ray absorptiometry. Following these techniques, obesity is considered to be body fat exceeding 25% for men and exceeding 32% for women. 

Apart from fat composition discussed above, fat distribution patterns can also indicate unhealthy weight. People who put on more of their excess weight above the waist (apple shape) are more at risk for cardiovascular disease than those who put it on below the waist (pear shape). For men, waist circumference above 40 inches is considered to be obese, and for women, that range is anywhere above 30 inches.

Overall, your energy balance will determine your body weight. That means if you eat more i.e. put in more calories than your expend, then you will gain weight. Likewise, if you eat less and burn more calories you will lose weight. Therefore maintaining a healthy body weight demands a balance between the amount of food you put in and the amount you burn. The energy we burn can be placed in three categories:

  1. Basal metabolic rate (BMR): The energy we burn when we are at rest. BMR is needed to drive basic processes in our body that we don’t even think about like blood circulation and breathing. BMR accounts for most of the energy we burn (60-75%). 
  2. Thermic effect of food: The heat energy produced during the process of digesting, absorbing, transporting and storage of food. This heat is used to warm the body. It accounts for 5-10% of energy burned.
  3. Energy cost of physical activity: The energy we expend through intentional exercise and all other physical movements including fidgeting. Accounts for 15-35% of energy burned.

BMR tends to be higher with:

  1. More lean body mass
  2. Greater height
  3. Younger age
  4. Higher thyroid hormone activity
  5. Sickness
  6. Being male
  7. Pregnancy and lactation
  8. Drugs and stimulants e.g. caffeine and nicotine 

Factors Affecting Body Weight 

If you are trying to change your body weight, it is important to identify the factors influencing it. This will tell you what you are up against and your chances of succeeding. Factors affecting body weight may be genetic, metabolic, physiological and sociocultural.

Genetic Factors

  1. The fat mass and obesity (FTO) gene: This is a “fat gene” that is associated with greater hunger and cravings for fat-building foods like sugar and refined starch. People with more of this gene will tend to gain weight easier 
  2. The thrifty gene: This is a gene that makes you burn less energy and is believed to have evolved to resist times of starvation. Therefore, if you have this gene then you are more likely to burn less fat and retain more weight 
  3. Drifty genes: These are certain genes that is believed to mutate (or drift), causing greater predisposition to obesity. People without these drifting genes tend to resist obesity  
  4. Set point hypothesis: This is the thinking that we all have a set-point or comfort zone. The body will always try to maintain that setpoint. Even if you lose or gain weight the body will always go back to its set point unless you continue to work hard to work against it. That is used to explain why most people eventually give up their diet and exercise, and return to their setpoint weight
  5. Protein leverage hypothesis: This is the thinking that people eat to meet their protein needs. Once we get enough protein we stop eating. If we substitute protein for high-carb foods that have little protein then we will tend to eat more of those foods until our protein need is met. Therefore the thinking is that people are overweight because of their protein-deficient diets

Metabolic Factors

  1. BMR: People with low BMR will tend to gain more weight
  2. Spontaneous physical activity (fidgeting): People who fidget less will retain more energy and hence gain more weight
  3. Sympathetic nervous system (SNS) activity: The nervous system directs various processes in our body. If the activity of SNS is low, then basal metabolic processes (BMR) will occur at a slower rate, increasing body weight
  4. Rate of use of fat for energy: We don’t all burn fat at the same rate. If you tend to use more carbohydrates for energy instead of fat, then you will likely gain more fat. On the other hand if your body is inclined to burn more fat for energy, you will store less and it will be easier to keep fat off
  5. Thyroid hormone activity: Low thyroid hormone production will lead to lower BMR and hence cause you to gain weight 
  6. Prescription medication: Some prescription medication can affect your BMR. Talk to your doctor if your medication is causing unwelcome weight gain or loss

Physiologic Factors

  1. Hypothalamus satiety center (HSC): The feeling of hunger is controlled by the HSC. This center is triggered when we are full and motivates us to eat less or stop eating
  2. Energy regulating hormones: (1) Accumulation of leptin in our adipose tissue cause us to reduce intake over time (2) Ghrelin hormone synthesized in the stomach increase appetite (3) Peptide YY hormone produced in the gastrointestinal tract reduces appetite and food intake
  3. Uncoupling proteins: Certain proteins in the inner membrane of the mitochondria are capable of disrupting ATP production resulting in less ATP production and more heat. Along with the lower ATP available for storage, the heat increases BMR and causes expenditure of more energy. Therefore, the more of these uncoupling proteins you have, the less chance you will be overweight or obese

Sociocutural Factors 

Weight gain may be due to a combination of overeating and inactivity. Modern technology provides less motivation to do strenuous physical work that burns energy. For example it is so much easier to pop a TV dinner in the microwave instead of cooking. Fear for personal safety, the lack of role models and cultural acceptance of body size may affect desire or motivation to exercise and manage weight. Weight gain has been paradoxically associated with people of poorer socioeconomic status. This may be due to exposure to more stress in their environment, inability to afford access to healthier foods including fruits and vegetables, and less time for personal self-care such as taking time to go to the gym on a regular basis.

Obesity is having excess body fat for a given height. A BMI of 30 to 39.9 kg/m2 is considered as obese, while BMI above that is considered as morbid (severe) obesity. Obesity is associated with other chronic diseases such as Type 2 diabetes and heart disease, as well as premature death. Hence, it is not surprising the heavy financial cost of this disease. The estimated annual medical cost of obesity in the US in 2008 was $147 million US dollars. Broken down, this translated to $1,429 higher medical cost compared to people with normal weight. 

The abdomen is a common place where many obese individuals carry their weight. Abdominal fat, as I mentioned in the previous lesson is closely linked to heart disease. That is because fat in this region increases blood lipid levels and also release signaling proteins called adipokines. These adipokines are known to increase inflammation which leads to a cluster of conditions called metabolic syndrome. The conditions include:

  1. Excess fat around the waste
  2. High blood lipid levels 
  3. High LDL (bad) cholesterol and low HDL (good) cholesterol levels
  4. High blood pressure 
  5. High blood sugar 

Several factors contribute to obesity. For example: 

  1. Biology: This include variables such as genetics, BMR and hormone levels 
  2. Physical Activity Environment: Accessibility to exercise facilities, which may be influenced by distance, cost and perceived safety. In addition, availability of labor-saving devises may reduce expenditure of physical labor  
  3. Exercise: Both intentional recreational activity and activity connected to occupation
  4. Psychology: Self-esteem, chronic stress
  5. Social Influences: Social acceptance of obesity, social pressure to overeat or indulge in alcohol consumption, and motivations to binge watch TV
  6. Food production: Available food variety, access to fast food, convenient packaging, cheap food formulations that values taste over nutrition, and influence of advertising

An effective treatment for obesity is a combination of eating of 500 to 1000 kcal less per day and exercising from 30 minutes to an hour, five days a week. Various weight loss medication has also been used to manage obesity (especially morbid obesity) but are not intended to replace proper diet and exercise. These medications work generally to suppress the appetite or increase satiety. However, they are not without side effects. Therefore, they should be used only under a physician’s supervision. For morbidly obese patients, bariatric surgery such as gastric banding and gastric bypass might be an option to consider, especially if they have life-threatening conditions such as heart disease and diabetes. This type of surgery can carry high long terms risks, so it is important to evaluate and be sure that the benefits outweigh the risks. Long term risks may include chronic diarrhea, vomiting, dehydration, food intolerance, nutritional deficiencies, gall stone, hernias and ulcers. 

Losing Weight and Keeping it Off Successfully 

There are three main strategies that you need to follow to lose weight and keep it off. 

  1. Eat less: The reduction should be reasonable and gradual. About 500 to 1000 kcal/day reduction is fine. More than that and you will feel like you are starving yourself too much. This is not sustainable for the long term. You may even be able to eat as much as you did before (in volume) by substituting high calorie foods on your plate for high fiber, nutrient-dense foods. This can be done easily by incorporating more fruits and vegetables in your diet. Don’t go below total calories of 1200 kcal/day or you may not be eating enough to support your BMR. Even though you are eating less, make sure your meals are balanced, having at least the recommended proportions of macronutrients according to the Acceptable Macronutrient Distribution Range (AMDR). Forget about fad diets that encourage you to cut an entire food group out of your diet or to overindulge in another e.g. any diet telling you to go low carb or to eat mostly fat or protein. Don’t sacrifice your overall health while you lose weight. Experts recommend weight loss of no more than 0.5 to 2 lbs a week.
  2. Exercise: Try to do at least 30-45 minutes of exercise every day of the week. This preferably should be intentional and focused at a certain time of the day whichever day and time works best for you. If not, try to eke out time to exercise at different times of the day. It may be a 3-minute break between work here or there but get it done with the scraps of time that you can find. For most of us who live busy lifestyles we would never exercise if we had to absolutely find a dedicated 30 minutes uninterrupted block of time each day
  3. Incorporating behavior-changing strategies: Maintaining good eating habits and exercise will only be sustainable if we also change behavior to support our new quest to keep the weight off. Think of some of the behavior you need to change to avoid getting overweight. Some strategies that may prove helpful include: planning grocery and meals ahead of time, saying no to social events that normally cause you to over-indulge, avoiding buffet-style restaurants, weighing/proportioning your meals, keeping a log of what you eat, rewarding yourself for meeting mini goals etc. Think of other things you could do. 

Gaining Weight 

So, what if you are on the other side of the spectrum? You are underweight and would like to gain weight. Being underweight is unhealthy just like being overweight. In fact, the underweight person may be less capable to cope and bounce back from illness compared to one who is somewhat overweight. Remember that during sickness, BMR increases leading to potential weight loss for which the already underweight person may not be able to cope or recover from. To gain weight, underweight individuals need to eat between 500 – 1000 kcal/day more than is required to maintain their present body weight. However, their diet must be, like any healthy diet, nutritious and balanced. In addition to diet, strength-training exercise must be included to build muscle mass. Forget about stuffing down protein supplements. You don’t need them to build muscle. Eating a regular balanced diet with an adequate amount of all three macronutrients is all you need with resistant training. For many skinny people, they are unable to increase weight because of their busy lifestyle which does not allow them time to prepare adequate meals. To avoid this problem they can plan ahead and make sure they always have adequate amounts of healthy to-go food with them. 

Reference: Thompson,&  J., Manore, M., Vaughan, L. (2020). The science of nutrition (5th ed.). New York. Pearson

Courtney Simons
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Courtney Simons is a food science writer. He holds a BS degree in food science and a PhD in cereal science from North Dakota State University.
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