Weight management

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

Weight management includes the techniques and 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, 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] However, weight neutral approaches to health have also been shown to result in positive health outcomes.[4][5]

Rising obesity rates are a major concern around the world. For example, about 60% of Americans and Canadians are either overweight or obese.[3][6] 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.[7]

Key concepts

There are many factors that contribute to a person's weight, including: diet, physical activity, genetics, environmental factors, health care support, medications, and illnesses.[3][8][9] 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.[8] 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.[8] 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[8][10]

The calories a person consumes come from both the foods and drinks they eat and drink.[8] 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 lose 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.[8]

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.[3][8][10] 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.[10] 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[10]

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[10]

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

Physical activity is one of the main components of a person's daily energy expenditure.[11] Physical activity can be related to a person's professional activities, it can be part of non-work related daily activities, or it can be in the form of physical exercise. Such physical activity may help a person to maintain a healthy weight and avoid developing noncommunicable diseases like diabetes, heart disease, and dyslipidemia (high cholesterol).[3][12] Increasing physical activity is particularly important following a diet to prevent catch-up fat according to the physiological concept of the Summermatter cycle.[13] Physical activity can encompass anything from gardening, cleaning, hiking, yoga, and stretching to kickboxing, strength training, or jogging.

Basal metabolic rate

Basal metabolic rate (BMR) is one of the main components of a person's daily energy expenditure.[11] BMR is defined as the amount of energy that is expended during a given amount of time by a person at rest.[11] 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.[11] 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.[11]

BMR is directly proportional to a person's lean body mass.[3][11] 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.[11] 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.[11] 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.[14]

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)[14]

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)[14]

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[14]

The Mifflin St. Jeor Equation was found to be the most accurate predictor of BMR compared to BMR measured by direct and indirect calorimetry.[14]

Body mass index

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]

${\displaystyle \mathrm {BMI} ={\frac {{\text{weight}}_{\text{kg}}}{{{\text{height}}_{\text{m}}}^{2}}}}$

or

${\displaystyle \mathrm {BMI} ={\frac {{\text{weight}}_{\text{lbs}}}{{{\text{height}}_{\text{in}}}^{2}}}\times 703}$

Though BMI is often 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)
Category[15] BMI
Underweight < 18.5
Normal Weight 18.5 – 24.9
Overweight 25.0 – 29.9
Obesity (Class I) 30.0 – 34.9
Obesity (Class II) 35.0 – 39.9
Obesity (Class III) ≥ 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.

Complicating factors

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][11] 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][11] 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]

Studies show that the most effective drugs for weight loss were phentermine and topiramate, pramlintide, naltrexone, bupropion, and liraglutide compared to placebo treatment, respectively. This provides new insights into anti-obesity drugs and hopes to shed new light on future research to manage and treat obesity.[16]

Orlistat (Xenical, Hoffmann-La Roche) is a powerful inhibitor of gastrointestinal lipase and as such, reduces fat absorption.[17]

Lifestyle modifications have had limited success, so careful physician-guided pharmacotherapy is ideal in combatting the obesity epidemic [18]

Diseases

There are several medical conditions that are associated with either weight loss or weight gain. Medical conditions associated with weight gain include hypothyroidism, Cushing's syndrome, Polycystic Ovary Syndrome (PCOS), and congestive heart failure.[19] On the other hand, unintentional weight loss can be due to disease and medical conditions such as cancer, gastrointestinal illness, psychiatric disorders, infections, endocrine disorders, and neurologic disorders. Common gastrointestinal disorders associated with weight loss are malabsorption due to Celiac disease or chronic pancreatitis. Depression and eating disorders such as anorexia nervosa are a common cause of weight loss. Infectious causes of weight loss include HIV/AIDS. While Type 1 diabetes has been found to cause weight loss, type 2 diabetes has been associated with weight gain. Other endocrine causes of weight loss include hyperthyroidism and chronic adrenal insufficiency.

Polycystic ovary syndrome (PCOS), which is characterized by insulin resistance and hyperandrogenism, is a common condition that has been linked to obesity. There appears to be a bidirectional relationship between obesity and PCOS, whereby PCOS increases the risk of obesity and similarly, obesity has been found to exacerbate and contribute to the development of PCOS.[20] A combination of genetics, lifestyle, and environment appear to contribute to the hormonal changes responsible for weight gain and obesity seen in individuals with PCOS.[20]

Obesity has been linked with pancreatic β-cell dysfunction and insulin resistance. In diabetes, impaired β-islet cells are responsible for the lack of blood glucose control. In individuals with higher body mass index concerning for obesity, there is increased hormones, proinflammatory markers, and glycerol, which contribute to insulin resistance. The combined effects of impaired pancreatic β-islet cells and insulin resistance increase one’s likelihood of developing diabetes.[21]

The importance of weight management in type 2 diabetes mellitus has been well studied. In individuals who have blood sugar levels considered to be in the prediabetic range, weight loss was demonstrated to have many benefits including improving glycemic control, reducing the risk of developing type 2 diabetes, and in some individuals even delaying or reversing its progression.[citation needed]

Although a cross-sectional study found that Black and Hispanic individuals have significantly higher odds of obesity and its related diseases, it is also important to note the role that social determinants of health and environmental factors contribute towards the disparity in obesity between racial groups. Social determinants of health that factor into barriers to weight management include food deserts,  low health literacy, lack of safe spaces to exercise outside, and lack of access to afforable health food.[22] However, the extent to which differences in genes may help explain disparities in obesity among different racial and ethnic groups warrants further investigation.[22]

Strategies

Increasing protein intake

A high protein diet relative to a low-fat or high-carbohydrate diet may increase thermogenesis and decrease appetite leading to a decrease in weight,[23] especially early in a diet (3–6 months) when rapid weight loss is observed.[24] However these advantages are reduced later in the diet (12–24 months) during the slow weight loss phase.[24]

Modifying plate size

Some studies have suggested that using smaller plates might help people to consume smaller portion sizes,[25] but this has since been shown to be ineffective.[26]

Modifying portion sizes, however, may be helpful in influencing energy intake.[27] 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.[27] 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.[27] 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.[27] 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.[28]

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.[29] When soup is consumed before a meal, there is a 20% decrease in the number of calories consumed during the meal.[30]

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.[7] 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.[31] 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.[31]

Eating more dairy

Studies have shown that a diet high in dairy decreases total body fat.[32] This occurs because a high amount of dietary calcium increases the amount of energy and fat excreted from the body.[33] Studies have shown that saturated, monounsaturated and polyunsaturated fats all have a higher excretion rate with a high calcium intake.[34] In these studies, a high calcium intake is considered 2300 mg and a low calcium intake is considered 700 mg.[34] 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.[34] Other studies specifically show that dairy sources of calcium demonstrate greater weight loss than supplemental calcium intake.[35] This may be due to the other bioactive components present in milk, which may aid in metabolic efficiency and fat loss.[35] 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.[36]

Incorporating more vegetables into meals

Fruits and vegetables have been shown to increase satiety and decrease hunger.[37] These foods have a low energy density, which is mainly due to the high water content and partly due to the fiber content.[37] 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.[37] Using apple cider vinegar with salads is also considered to help reduce fat.[38]

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.[39] Dietary fiber consists of non-digestible carbohydrates and lignin, which are a structural component in plants.[40] Fiber recommendations range from 10 – 13 grams/1000 calories, with slightly higher recommendations for men.[41]

Due to the high volume or water content of fiber-rich foods, fiber displaces available calories and nutrients from the diet.[42] Consumption of viscous fibers delays gastric emptying, which may cause an extended feeling of fullness.[43] 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.[44] In addition, hormone secretion is affected during fiber ingestion.[45] Insulin response is reduced and cholecystokinin (CCK) in the small intestine is increased.[39] Insulin regulates blood glucose levels while CCK adjusts gastric emptying, pancreatic secretion and gall bladder contraction.[39] There is direct correlation between CCK and satiety after foods of different fiber contents are consumed.[46] Fiber may have the added benefit of helping consumers decrease food intake throughout the day. However, the 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.[47]

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.[48] 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.[48][49][50][51] The increase in gut hormones can affect long-term energy balance by affecting neuronal pathways in the brain[52][53] as well as improved overall health of the intestines.[54] Based on developing research, consumption of resistant starch can be an effective means of weight management.

Increasing caffeine intake

Caffeine and black coffee have been associated with increased energy expenditure and subsequent weight loss.[55] Caffeine belongs to a class of compounds called methylxanthines, and is present in coffee, tea, cocoa, chocolate and some cola drinks.[56] Caffeine induces a thermogenic effect in the body by increasing sympathetic nervous system activity, which is an important regulator of energy expenditure.[57][58][59]

Increasing green tea intake

Green tea has been associated with decreasing blood glucose,[60] inhibiting hepatic and body fat accumulation,[60][61] and stimulating thermogenesis[62] due to the catechins that are present. Catechins are polyphenols that are a major component of green tea extract.[63] Green tea has also been shown to increase energy expenditure and fat oxidation in humans, independent of the caffeine content.[62][64] 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.[65] Moreover, catechins in the brain play a major role in satiety.[66]

Popular diets

As weight loss depends on calorie intake, different kinds of calorie-reduced diets, such as those emphasising particular macronutrients (low-fat, low-carbohydrate, etc.), have been shown to be no more effective than one another as weight loss tools.[67][68][69][70][71] Weight regain is common, and the outcome of a diet can vary widely depending on the individual.[68][71][72]

DASH diet

The Dietary Approaches to Stop Hypertension (DASH) diet focuses on increasing the consumption of fruits, vegetables, and low-fat dairy products while also decreasing the consumption of red meats, sugary drinks, and foods high in total or saturated fats. This food program was founded during the DASH clinical trials of 1997, which spanned across 4 different sites and included both hypertensive and normotensive people. As a result of these studies, this diet was shown to decrease or control blood pressure when compared to the typical U.S. diet.[73][74] These large-scale, randomized control trials trials suggest that DASH offers an intervention to manage elevated blood pressures and prevent cardiovascular disease non-pharmacologically.[74][75][76][77] In addition, combining the DASH diet with a reduced sodium intake will further decrease blood pressure, but is not required for therapeutic effect. This is because it has been proven to be effective at a wide range of sodium intake levels.[73] More recent reviews of DASH have continued to advocate its efficacy as an affordable weight loss tool, but stress that diet adherence is key to produce the desired results.[78] According to the Mayo Clinic, those who wish to follow this program should aim for an intake of:[79]

• 7-8 daily servings of grains
• 4-5 daily servings of vegetables
• 4-5 daily servings of fruits
• 2-3 daily servings of fat free dairy
• 2 or less daily servings of meat, poultry, or fish
• 4-5 weekly servings of nuts, seeds, and dry beans
• 5 weekly sweets

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