# Weight management

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Nutrition is an important part of maintaining a healthy body weight.

Weight management is the phrase used to describe both the techniques and underlying physiological processes that contribute to a person's ability to attain and maintain a certain weight. Most weight management techniques encompass long-term lifestyle strategies that promote healthy eating and daily physical activity.[1] Moreover, weight management involves developing meaningful ways to track weight over time and to identify ideal body weights for different individuals.[2]

Due to the rising obesity rates in many parts of the world, proper weight management strategies most often focus on achieving healthy weights through slow but steady weight loss, followed by maintenance of an ideal body weight over time.[3]

Rising obesity rates are a major concern around the world, especially in North America. About 60% of Americans and Canadians are either overweight or obese.[3][4] Understanding the basic science of weight management and some of the strategies for attaining and maintaining a healthy weight is very important to a person's overall health because obesity is a risk factor for many chronic diseases, like Type 2 diabetes, hypertension and cardiovascular disease.[5]

## Key components of weight management

There are many factors that contribute to a person's weight, including: diet, physical activity, genetics, environmental factors, medications, and illnesses.[6][3] Each of these factors affect weight in different ways and to varying degrees, but health professionals most often stress the importance of diet and physical activity above all other factors because they can be affected by conscious behavior modification.[6] The following is a review of some of the key components of weight management in humans.

### Energy Balance

The science behind weight management is complex, but one of the key concepts that governs weight management is Energy Balance. Energy Balance is the phrase used to describe the difference between the number of calories a person consumes and the number of calories that same person expends (a.k.a. burns) in a given time period.[6] There are three possible scenarios when it comes to the energy balance equation:

• Calories consumed (food, drink) = Calories expended (basal metabolic rate, physical activity, thermogenic effect of food, acute illness)
• Outcome: Weight remains unchanged
• Calories consumed > Calories expended
• Also known as Positive Energy Balance
• Outcome: Weight increases
• Calories consumed < Calories expended
• Also known as Negative Energy Balance
• Outcome: Weight decreases[6][7]

The calories a person consumes come from both the foods and drinks they eat and drink.[6] The calories a person expends comes from their basal metabolic rate and their daily physical activity.[3] When eating a healthy diet mainly composed of vegetables, lean meats, and fruits, the human body is very good at maintaining a neutral energy balance so that calories consumed do not substantially exceed calories expended in a given time period and vice versa.[3] This energy balance is regulated by hormones like Leptin (suppresses), Ghrelin (stimulates), and Cholecystokinin (suppresses) which either suppress or stimulate appetite.[3] This unconscious regulation of energy balance is one of the factors that make sustained weight loss very difficult for many people. That being said, consuming fewer calories than the numbers of calories expended each day is fundamental to weight loss in both the short and long term. If attempting to loss weight, the National Heart, Lung, and Blood Institute (NHLBI) recommends a slow and steady approach by eating 500 fewer calories than the number of calories burned or expended each day.[6]

Photo of a healthy salad with chicken, nuts, and strawberries.

### Diet

As previously stated in the Energy Balance section above, quantity of food and drink consumed by an individual plays a very important role in weight management. Additionally, the types of food and drink a person consumes are also very important to weight management.[6][3][7] Not only is it important to eat a well balanced diet in order to get the proper amount of vitamins and nutrients each day to prevent illness, but it is also important to be aware that certain qualities of foods and drinks (for example: energy density, palatability, sugar content) can have profound effects on weight by affecting hunger and satiety in different ways.[3] For example, sugary drinks like sodas are very palatable and contain a significant number of calories but do little to affect satiety. In other words, drinking sugary drinks does not help get rid of hunger but still adds many calories to a person's diet which can lead to overeating, positive energy balance, and weight gain.[3]

The United States Department of Agriculture and United States Department of Health and Human Services attempt to provide evidence based recommendations for the types and amounts of certain foods people should eat to maintain a healthy diet in a document called The Dietary Guidelines for Americans.[7] These recommendations are updated every 5 years and the most recent version (2015-2020 Dietary Guidelines for Americans) recommends the following:

Eat a diet that is primarily composed of:

• A diverse selection of vegetables - like dark and leafy greens, red and orange vegetables, legumes (beans and peas)
• Whole fruits
• Whole grains
• Low fat and fat free dairy products - like milk, yogurt, and cheese
• Foods high in protein like lean meats, seafood, poultry, eggs, and legumes, nuts, seeds, and soy products[7]

Avoid or limit the following items:

• Trans fats
• Saturated fats - should not exceed 10% of total daily calories
• Added sugars - should not exceed 10% of total daily calories
• Salt - should consume less than 2,300 mg of salt per day
• Alcohol - limited to 1 drink per day for women and 2 drinks a day for men[7]

Some of these recommendations have been called into question since they were released; however, most health professionals agree that a diet that is primarily composed of vegetables, leans meats, whole fruits, whole grains, nuts, and seeds is ideal for maintaining a healthy weight and overall health.[3]

### Physical Activity

This image depicts proper running mechanics.

Physical activity is one of the main components of a person's daily energy expenditure.[8] Physical activity can be broken down into the following types of activities:

• Work/occupation related physical activity
• Exercise related physical activity
• Non-work and non-exercise related physical activity (activities of daily living)[3]

It is important to remain physically active in all three domains listed above in order to maintain a health weight and avoid developing noncommunicable diseases like diabetes, heart disease, and dyslipidemia (high cholesterol).[3][9] It can be difficult to be physically active in every area of a person's life, due to things like occupation, physical fitness level, and living environment, but increasing physical activity whenever possible can help offset times of inactivity and can lead to better weight management and overall health.[3][9]

As part of the Dietary Guidelines for Americans, the United States Department of Agriculture and United States Department of Health and Human Services releases evidence based physical activity recommendations in a section titled Physical Activity Guidelines for Americans.[9]

This section recommends the following for children (6–17 years old):

• At least 60 minutes of physical activity per day
• Most of their physical activity should be aerobic based with vigorous aerobic exercise 3 time per week
• Participate in strength building physical activity 3 time per week.

This section recommends the following for adults (18–64 years old):

• Avoid physical inactivity whenever possible
• At least 150 minutes (2 hour and 30 minutes) of moderate intensity exercise per week OR 75 minutes (1 hour and 15 minutes) of vigorous intensity exercise per week
• Exercise should be spread out throughout the week
• Exercise a minimum of 10 minutes at a time
• Progressively increase physical activity to 300 minutes (5 hours) or more of moderate intensity exercise per week OR 150 minutes (2 hours and 30 minutes) or more of vigorous intensity exercise per week
• Participate in full body weight training exercise 2 time per week[9]

This section recommends the following for older adults (${\displaystyle \geq }$65 years old):

• Same guidelines as adults (listed above) but modified to accommodate their level of physical fitness and chronic conditions
• Focus on physical activity that improves balance[9]

### Basal Metabolic Rate (BMR)

Basal Metabolic rate (BMR) is one of the main components of a person's daily energy expenditure.[8] BMR is defined as the amount of energy that is expended during a given amount of time by a person at rest.[8] In other words, it is the amount of energy a person's body uses to do things like pump blood, maintain proper brain function, breakdown toxins, and ensure other bodily functions. Technically speaking, BMR is the amount of energy the body expends during the following very specific conditions: right after waking up, while in a resting state, and after fasting for 12–14 hours.[8] Sometimes the term Resting Metabolic (RMR) is used in place of BMR but RMR is slightly different in that it is not measured under the previously listed stringent conditions and is about 10% more than BMR.[8]

BMR is directly proportional to a person's lean body mass.[3][8] In other words, the more lean body mass a person has, the higher their BMR. BMR is also affected by acute illnesses and increases with conditions like burns, fractures, infections, fevers, etc.[8] BMR can be measured via direct and indirect calorimetry; however, it is possible to estimate a person's BMR using one of several equations that use a person's age, sex, height, and weight to calculate a fairly accurate estimate of a person's BMR.[8] Some of the most popular and accurate equations used to calculate BMR are the original Harris-Benedict equations, the revised Harris-Benedict equations, and the Mifflin St. Jeor equation.[10]

The original Harris-Benedict Equations are as follows:

• BMR (Males) in Kcals/day = 66.47 + 13.75 (weight in kg) + 5.0 (height in cm) - 6.76 (age in years)
• BMR (Females) in Kcals/day = 655.1 + 9.56 (weight in kg) + 1.85 (height in cm) - 4.68 (age in years)[10]

The revised Harris-Benedict Equations are as follows:

• BMR (Males) in Kcals/day = 88.36 + 13.40 (weight in kg) + 4.8 (height in cm) - 5.68 (age in years)
• BMR (Females) in Kcals/day = 447.59 + 9.25 (weight in kg) + 3.10 (height in cm) - 4.33 (age in years)[10]

The Mifflin St. Jeor Equation is as follows:

• BMR (Males) in Kcals/day = 9.99 (weight in kg) + 6.25 (height in cm) - 4.92 (age in years) + 5
• BMR (Females) in Kcals/day = 9.99 (weight in kg) + 6.25 (height in cm) - 4.92 (age in years) - 161[10]

The Mifflin St. Jeor Equation was found to be the most accurate predictor of BMR compared to BMR measured by direct and indirect calorimetry.[10]

### Thermogenic Effect of Food

The thermogenic effect of food is another component of a person's daily energy expenditure and refers to the amount of energy it takes the body to digest, absorb, and metabolize nutrients in the diet.[3][8] The amount of energy expended while processing food differs by individual but on average it amounts to about 10% the number of calories consumed during a given time period.[3][8] Processing proteins and carbohydrates has more of a thermogenic effect than does processing fats.[3]

### Genetics

Genetics play an important role in weight management and contribute to a person's risk of becoming obese.[3] In fact, several genes have been found to be associated with elevated Body Mass Index (BMI) and obesity.[3] That being said, genetics can only be blamed for a small portion of a person's excess weight as there are many other significant factors that affect a person's weight, as discussed in the sections above.[3]

There are some rare genetic disorders that do cause significant weight gain like Prader-Willi Syndrome.[3]

### Medications

Certain medications can cause either weight loss or weight gain. These side effects are often listed for each medication and should be considered when attempting to manage a person's weight.[3]

### Diseases

As previously stated, acute illnesses can effect weight management by increasing a person's BMR.[8] There are also several other medical conditions that are associated with either weight loss or weight gain. Examples of conditions that are associated with weight gain include hypothyroidism and Cushing's Syndrome.[3] Examples of conditions that are associated with weight loss include hyperthyroidism and many cancers.[3]

## Body Mass Index (BMI)

Body Mass Index (BMI) is a value used to get a general sense of a person's overall mass and is calculated using a person's height and weight.[3] It is more often used than weight alone to determine if an individual is underweight, normal weight, overweight, or obese. The following two equations can used to calculate BMI depending on the units used for height (meters vs. inches) and weight (kilograms vs. pounds):[3]

BMI = Weight (kg) / Height2 (m2)

OR

BMI = [ Weight (lbs) / Height2 (in2) ] x 703

Though BMI is often times used to help assess for excess weight, it is by no means a perfect representation of a person's body fat percentage.[3] For example, an individual can have a higher than normal BMI but have a normal body fat percentage if they have higher than average muscle mass because excess muscle contributes to a higher weight. The following table shows how different ranges of BMIs are often categorized into underweight, normal weight, overweight, and obese:[3]

Classification of Overweight and Obesity by Body Mass Index (BMI)
Obesity Class BMI
Underweight ${\displaystyle <}$ 18.5
Normal Weight 18.5 - 24.9
Overweight 25.0 - 29.9
Obesity I 30.0 - 34.9
Obesity II 35.0 - 39.9
Extreme Obesity III ${\displaystyle \geq }$40.0

Since BMI is not a perfect representation of a person's body fat percentage, other measurements like waist circumference are often used to better assess for unhealthy excess weight as it pertains to body fat.[3] Despite not being a perfect representation of healthy and unhealthy weight, BMI is very important value because it helps health professionals identify people who are at higher risk of developing illnesses like diabetes, hypertension, dyslipidemia (high cholesterol), liver disease, and some cancers.[3] In general, as BMI increases so too does a person's risk of developing those previously stated illnesses.[3] Additionally, regularly calculating a person's BMI can also be used to help track changes in a person's body mass over time.

## Strategies for maintaining a healthy weight

### Increasing protein intake

The satiating property of dietary protein is influenced by when the protein is consumed. Studies have shown that protein intake at breakfast has a greater effect on satiety than during later meal times.[11] There are several explanations as to why this is the case. Firstly, protein has a greater thermogenic effect than carbohydrates and fat, which enables the body to burn more calories.[12] Secondly, a high protein breakfast appears to slow gastric emptying, which attributes to the fact that protein appears to be the most satiating macronutrient.[13] Finally, a high protein breakfast increases the activity of glucagon,[13] which activates the pathways for glucose synthesis. One study showed that fat loss was approximately twice as much in the high-protein diet group than the moderate-protein diet group in overweight and obese individuals.[12]

### Modifying plate size

Using smaller plates helps to consume smaller portion sizes which leads to the consumption of fewer calories.[14] Studies have shown that portion size influences energy intake.[15] People who are presented with larger portions do not report to have a higher level of satiety, which suggests that hunger and satiety signals are ignored when a large portion of food is placed in front of them.[15] In particular, one study showed that participants consumed 31% less calories with the small portion sized of a 6-inch submarine sandwich compared with the large portion size of a 12-inch submarine sandwich.[15] Increased portion sizes have occurred simultaneously with the increase in obesity rates; hence, large portion sizes can be one of the factors contributing to the current increase in average body weight in the US.[15] Evidence from a systematic review of 72 randomized controlled trials indicates that people consistently eat more food when offered larger portion, package, or tableware sizes rather than smaller size alternatives.[16]

### Eating more soup

Soups have a significant effect on satiety. Studies have demonstrated that when compared to solid foods, soup ingestion decreases the amount of energy intake.[17] When soup is consumed before a meal, there is a 20% decrease in the number of calories consumed during the meal.[18]

### Choosing low-calorie foods

A moderate decrease in caloric intake will lead to a slow weight loss, which is often more beneficial for long term weight management vs rapid weight loss.[19] For example, choosing a black coffee instead of a full fat latte will save calories that will add up in the long run. Low fat meats reduce the total amount of calories and cholesterol consumed.[20] For example, traditional beef patties have 19.2% fat and 272 kcal per 100 g of meat. On the other hand, lean beef patties have 9.8%fat and 196 kcal.[20]

### Eating more dairy

Studies have shown that a diet high in dairy decreases total body fat.[21] This occurs because a high amount of dietary calcium increases the amount of energy and fat excreted from the body.[22] Studies have shown that saturated, monounsaturated and polyunsaturated fats all have a higher excretion rate with a high calcium intake.[23] In these studies, a high calcium intake is considered 2300 mg and a low calcium intake is considered 700 mg.[23] A possible explanation to this phenomenon is that high intakes of calcium cause calcium soap formation and/ or binding of bile acids in the intestine.[23] Other studies specifically show that dairy sources of calcium demonstrate greater weight loss than supplemental calcium intake.[24] This may be due to the other bioactive components present in milk, which may aid in metabolic efficiency and fat loss.[24] The accuracy of this statement remains controversial. Since most natural dairy products contain fat content, there is a common understanding that this may cause weight gain. In addition, dairy contains some key ingredients such as whey protein and combinations protein/calcium that have a positive effect on satiety, increases energy loss, and finally assists weight loss.[25]

### Incorporating more vegetables into meals

Fruits and vegetables have been shown to increase satiety and decrease hunger.[26] These foods have a low energy density, which is mainly due to the high water content and partly due to the fiber content.[26] The reduction of energy density has been shown to enhance satiety. The water adds weight, without adding calories and the fiber slows gastric emptying. Both of these factors contribute to the satiating effect of vegetables and fruits. Studies have also shown that fiber decreases hunger and also decreases total energy intake.[26]

### Increasing fiber intake

Dietary fiber has been suggested to aid weight management by inducing satiety, decreasing absorption of macronutrients and promoting secretion of gut hormones.[27] Dietary fiber consists of non-digestible carbohydrates and lignin, which are a structural component in plants.[28] Fiber recommendations range from 10 – 13 grams/1000 calories, with slightly higher recommendations for men.[29]

Due to the high volume or water content of fiber-rich foods, fiber displaces available calories and nutrients from the diet.[30] Consumption of viscous fibers delays gastric emptying, which may cause an extended feeling of fullness.[31] Satiety is also induced by increasing chewing, which limits food intake by promoting the secretion of saliva and gastric juice, resulting in an expansion of the stomach.[32] In addition, hormone secretion is affected during fiber ingestion.[33] Insulin response is reduced and cholecystokinin (CCK) in the small intestine is increased.[27] Insulin regulates blood glucose levels while CCK adjusts gastric emptying, pancreatic secretion and gall bladder contraction.[27] There is direct correlation between CCK and satiety after foods of different fiber contents are consumed.[34] Fiber may have the added benefit of helping consumers decrease food intake throughout the day. However, results of trials examining this possibility have been conflicting. In general, large intakes of dietary fiber at breakfast are associated with less food intake at a lunch.[35]

### Increasing resistant starch intake

Resistant starch is a type of non-digestible, fermentable fiber that is resistant to amylase digestion in the small intestine, and is broken down to short-chain fatty acids by microflora in the large intestine. It is commonly found in cooked and cooled potatoes, green bananas, beans and legumes.[36] Resistant starch dilutes energy density of food intake, has a bulking effect similar to non-fermentable fiber, and increases the expression of PYY and GLP-1 in the gut.[36][37][38][39] The increase in gut hormones can affect long-term energy balance by affecting neuronal pathways in the brain[40][41] as well as improved overall health of the intestines.[42] Based on developing research, consumption of resistant starch can be an effective means of weight management.

### Capsaicin

Clinical research on capsaicin has showed that consumption of the spice during breakfast can increase energy expenditure by 23% immediately after meal ingestion.[43] Capsaicin, also known as hot pepper, is a primary ingredient in chilli peppers and red hot peppers.[44] Hot peppers have been reported to induce thermogenesis at the cellular level.[45][46]

As well, capsaicin induces satiety as a result of oral and gastro-intestinal contribution.[44] Lower energy and fat intake were observed under short-term conditions; however, the effect of the spice was reduced over prolonged exposure. Increased satiety was observed when oral contribution of capsaicin was measured in addition to the gastro-intestinal exposure, indicating the sensory effect of hot peppers plays a significant role.[44]

### Increasing caffeine intake

Caffeine and black coffee have been associated with increased energy expenditure and subsequent weight loss.[47] Caffeine belongs to a class of compounds called methylxanthines, and is present in coffee, tea, cocoa, chocolate and some cola drinks.[48] Caffeine induces a thermogenic effect in the body by increasing sympathetic nervous system activity, which is an important regulator of energy expenditure.[49][50][51]

### Increasing green tea intake

Green tea has been associated with decreasing blood glucose,[52] inhibiting hepatic and body fat accumulation,[53][54] and stimulating thermogenesis[55] due to the catechins that are present. Catechins are polyphenols that are a major component of green tea extract.[56] Green tea has also been shown to increase energy expenditure and fat oxidation in humans, independent of the caffeine content.[55][57] In a human study conducted, 690 mg of catechins daily for 12 weeks reduced body fat, suggesting that green tea might be useful in the prevention of chronic disease, particularly obesity.[58] Moreover, catechins in the brain play a major role in satiety.[58][59]

## Popular diets

When assessing popular diets, a person's food preferences, lifestyle and medical conditions should be taken into account when choosing the correct diet. Adherence level to the diet is a bigger determinant of clinical benefits over the diet type itself.[60] "Dieting" needs to be a lifestyle change rather than for a short term amount of time.

### Weight Watchers

Weight Watchers offers a variety of dieting products and services to assist weight loss and maintenance by a calorie restricting method. Weight watchers promote healthy habits, a supportive environment, exercise and healthy food choices.[61] A member to selects a goal weight that will result in a body mass index (BMI) generally accepted as healthy (18 – 24.9).[61] Participants are encouraged to produce a rate of weight loss up to 2 pounds per week.[61] Their food guide promotes food choices that not only reduce calories, but also meet nutritional recommendations.[61] Exercise is also recommended for weight loss and is incorporated into their points system. They use a point system that incorporates calories, fat, and dietary fiber content of each food. People are given a certain number of points they are supposed to consume each day.[61]

Strengths

• Their food guide promotes food choices that reduce calories, and also meet nutritional recommendations.
• They construct an activity plan along with nutritional guidelines to encourage exercise.
• They offer support and encouragement through weekly meetings
• Is a slower weight loss than other more restrictive diets. This seems like a weakness, but most medical authorities recommend keeping weight loss at 1–2 pounds a week.

Limitations

• Can be quite expensive over time

### The Atkins Diet

The Atkins Diet involves the restriction of carbohydrates in one's diet causing the body's metabolism to switch from burning glucose as fuel to burning stored body fat, sending the body into a state of ketosis.[62] Ketosis causes a person to get their energy from ketones, which also causes them to feel less hungry.[62] Carbohydrate consumption must be <40 grams/day (= 2 slices of bread) for ketosis to occur.[62]

Strengths

• Allowed to eat rich foods
• When in ketosis, people feel less hungry and more satisfied

Limitations

• Ketosis causes unusual breath odor and constipation
• There is worry that the diet promotes heart disease and there is a potential loss of bone and it is not recommended for people with liver and kidney problems due to the high amounts of protein.
• The preferred source of energy for the brain is glucose, which is decreased in a low-carbohydrate diet

### GM Diet

The GM Diet was devised by the company General Motors to help its employees deal with weight gain due to sedentary work environment and achieve weight loss. The diet consists of low carbohydrates (they are primary fuel for anaerobic metabolism and strength training, a drastic depletion causes health risks) a 5–10g/kg body-weight which includes high fiber – nutrient dense starch whole foods for slow energy release and to increase satiety with fruits, tubers, vegetables...etc., a moderate protein intake of 1.5–2.0g/kg body-weight along with 20-30g healthy fats daily (it supports natural hormonal and enzymatic functioning, improves insulin sensitivity, dilate blood vessels), drinking plenty of water and abstaining from alcohol (empty calories). The GM Diet works by burning off fat stored in body through creating a calorie deficit, with daily intake of required proportioned calorie amount, to ensure homeostatic balance.

Regular exercise is required to maintain the state of recovery from weight loss management. If resistance training is employed to maintain muscle mass for better glucose-disposal and glucose-control capability, a 12 to 48 hours of rest between sessions is a required time for the muscles to recover depending on intensity of exercise or training load.[63][64] A change in hormone levels occurs in case of drastic dietary changes, like leptin - a satiety hormone, made by fat cells showed declination in levels, its function is to regulate energy balance by inhibiting hunger and at the same time, there is also a rise in levels of ghrelin - a hormone secreted in the gastrointestinal tract when a person's stomach is empty and informs one they are hungry. Changes in production of these hormones along with other satiating hormones in extreme weight loss managements showed suppressed resting metabolic rate (RMR) which resulted many subjects regaining much of the lost weight.[65]

### Ornish Diet

The Ornish Diet is a fat restricting diet (less than 10% of calories from fat) focusing on eating high amounts of fiber, and following a low-fat vegetarian diet.[66] The Ornish diet recommends combining the diet with exercise that allows the body's fat burning mechanism to work most effectively.[66] The philosophy is focused less on restricting calories but by watching the ones consumed, by recommending foods that can be eaten all the time, some of the time and none of the time.[66]

Foods that can be eaten whenever hungry until one is full are:

• Beans and legumes, fruits, grains and vegetables

Foods eaten in moderation are:

• Nonfat dairy products – skim milk, nonfat yogurt, nonfat cheese, nonfat sour cream and egg whites

Foods to avoid

• Meats of all kinds – if can't give up, only eat minimally
• Oils and oil-containing products (margarine and most salad dressings)
• Avocados, olives, nuts and seeds, dairy products (other than non-fat ones)
• Simple sugar and simple sugar derivatives (honey, molassess, corn syrup, and high-fructose syrup)
• Alcohol
• Anything commercially prepared that has more than 2 grams of fat per serving

Suggests eating a lot of little meals because this diet makes people feel hungry more often, which will help them feel full faster and eat more food without increasing the number of calories.[66]

Strengths

• Does not restrict calories
• Doesn't slow down metabolism
• Recommends regular exercise, yoga and meditation along with the diet
• Has been associated with a reversal of coronary blockage

Weakness

• Very restrictive
• People will feel hungrier and need to eat more food (but less calories)

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