In the US rates of overweight and obesity are still rising. In 2020 42 % of Americans were obese and half of the American population reports to be on a weight loss journey. On the other hand a culture of constant food tracking has emerged. How does our body know how much to eat? Is it necessary to track all our food with an app to maintain a healthy weight? During this chapter you will explore the components of the energy balance, how we determine healthy weight and learn about weight gain, loss and weight maintenace.

The images in this chapter are included under the provisions of fair use under U.S. copyright law (non-profit, educational use).

1. Energy Balance Is the Relationship Between Energy Intake and Energy Expenditure

On the most basic level, energy balance describes the relationship between energy intake from our daily meals and the energy our body uses, called the energy expenditure. When energy intake equals energy expenditure our weight is stable.

The metabolic state when energy intake is higher than the expenditure is called positive energy balance. The additional energy is stored as glycogen (glucose storage) or fat in the adipose tissue. Weight increases.

If the energy intake is lower than the energy expenditure the metabolism taps into the energy resources. Weight will decrease.

While this premesis of the energy balance is in principle correct it does not work 100 % like that. Our body is extremely energy inefficient. Food energy is converted into ATP and the ATP is used for muscle contractions, pumping minerals across cell membranes, transporting, synthesizing and so much more. Only 25 % of the chemical energy in our food is used to move and maintain our bodies.

75 % is lost as heat energy. This also means that the metabolism can become more energy efficient if necessary. For example, if you are fasting metabolic adaptions will increase the energy efficiency and you will be able to complete the same amount of work using less energy. On the opposite end if you eat slightly more than usual the metabolism will slightly increase the BMR and heat production.

That way our body maintains body weight, called set-point weight. Only if the energy imbalance is consistently positive or negative our body will increase or decrease weight.

The Energy Expenditure Has Several Components

The energy expenditure has four main components:

• Basal metabolic rate: Energy expended when the body is in a fasted—over 12 hours of no food intake—resting state (no movement, lying still) in a warm, quite environment. When scientists measure BMR the long fasting period makes it necessary to start the test in the morning which complicates research. Therefore there is also an relaxed version of the BMR, the resting metabolic rate or RMR for short. The RMR is still measured in a resting position in a warm quiet environment but the fasting period is shorter (3 – 4 hours) and slight movement is allowed. The RMR is about 6 % higher than the BMR.
• Physical activity has two sub-components. NEAT or non-exercise activity thermogenesis is any type of light physical activity during the day while exercise related energy expenditure refers to structured exercise.
• TEF or thermic effect of food measures energy used to digest, absorb and metabolize food.
• Cold-induced thermogenesis refers to energy used to keep the body warm during cold temperatures.

The BMR or RMR are measured using either direct or indirect calorimetry. During direct calorimetry the person is placed into a small room, the metabolic chamber. The heat the body radiates is measured and then converted into kcal. Indirect calorimetry uses a mask to measures to oxygen uptake and CO2 exhalation.

The BMR and RMR include the energy use of organs such as liver, brain activity, heart pumping blood, kidneys producing urine. Even the skeletal muscles need to maintain homeostasis during rest which requires ATP.

The BMR can vary 25 to 30 % between individuals. Factors influencing the BMR/RMR are:

• Since muscle fibers are metabolically active even at rest increasing lean body mass (muscle) will increase the BMR.
• Size also matters. A taller person will have a larger body surface resulting in a higher BMR. Higher lean mass and larger body surface means that men have a higher BMR than women.
• People with a higher body temperature are less energy efficient which increases the BMR.
• Thyroid hormones can up-or downregulate energy expenditure (40 % – 50 %). So does nervous system activity and the use of tobacco and caffeine.
• The BMR/RMR decreases slightly—1 – 2 % per decade—with age after age 30.
• The energy balance also impacts the BMR. Fasting or weight loss starts metabolic adaptions that increase the efficiency of the energy metabolism. This can mean a 10 – 20 % reduction when the body enters conservation mode during weight loss.

Studies determining the BMR in a range of people came up with a formula that allows us to estimate the BMR for men and women. In average women need 0.9 kcal/kg/hour while men need 1 kcal/kg/hour. Keep in mind that the BMR can vary 25 – 30 %.

Physical activity can range widely and has two components. NEAT or non-exercise activity thermogenesis includes our every day physical activity. Laying in bed, we still move a little even in our sleep. Standing, walking around, climbing stairs, cleaning and more increase the energy expenditure. Even if we are sitting still on the sofa, watching our favorite show, we will fidget and contract muscles.

Exercise is the second component and the energy expenditure can vary widely depending on the time spent exercising as well as intensity and type of exercise. The amount of muscles mass also plays a role in how much energy is expended during an excercise session. Larger muscles will expend more energy.

Every time we eat hormones signal to synthesize enzymes, transport proteins and digestive juices. Many nutrients use ATP dependent active transport to pump the nutrient across cell membranes. Once all nutrients are metabolized and stored the metabolism returns to an equilibrium. Post-prandial processed require energy in form of ATP. This increase in energy expenditure is called the thermic effect of food or TEF.

The TEF is a relatively small component of the energy expenditure and ranges between 5 and 10 % of our daily energy expenditure. The TEF depends of course on the amount of food eaten since more food requires more energy to digest.

The TEF also varies with the food composition. Protein-rich foods require about 20 – 30 % of the energy expenditure, while carbohydrate-rich foods require 5 – 10 % of the energy expenditure. The least amount of TEF is required when fat-rich foods are eaten. Triglycerides do not need to be converted into other nutrients but can be easily and efficiently stored in the adipose tissue right after absorption.

The smallest component of the total energy expenditure (TEE) is the cold-induced thermogenesis. This can inlude shivering, muscle tensing and fidgeting when temperatures drop and we are starting to get cold.

Humans also have special adipose tissue that produces rather heat than storing large amount of energy. This type of adipose tissue is called beige and brown adipose tissue. It looks brown (or beige) under the microscope because it contains many mitochondria. Newborns have larger amounts of brown adipose tissue but as the infant grows it is turned into white, fat storing adipose tissue. Adults have only small amounts left. White adipose tissue can be turned beige (increasing mitochondria) due to cold exposure and intense exercising.

People with more beige and brown adipose tissue maintain body weight easier. There seems to be a genetic component determining amounts.

2. Determining a Healthy Weight Is More Complex Than Stepping On a Scale

When we visit the physician’s office we immediately are ushered to the scale. Our height and weight is then used to determine the BMI. While the weight is necessary so the physician can estimate the dose for a medication, the BMI is also used to gauge if we are at a healthy weight. You also might have heard that the BMI is not reliable, does not work. The question is if this is true, why do physicians still use the BMI and why didn’t we come up with something better.

The BMI is a reasonable, quick tool to gauge disease risk for most people. But, anybody using it needs to fully understand how to use the BMI properly. First, the BMI does not work for everybody. Healthcare providers should not use the BMI to determine disease risk for very short individuals (< 5 ft), very tall individuals, children and the elderly.

Second, the BMI is based on weight and height. That means that the BMI does not distinguish between fat and muscle mass. Very muscular people will end up with a high BMI not reflective for their health status, sometimes even be classified as obese.

For everybody else the BMI is a good and practical screening tool. Screening tool means that health risk should not be solely determined by the BMI result, but trigger a conversation about eating, exercise and other health behaviors followed by some lab tests.

The BMI is calculated by dividing the body weight in kilogram by the squared height. The slide above also shows the formula when you work with pounds and inches.

How do you interpret the BMI. The BMI is categorized into three groups: Underweight, healthy weight, overweight and obese. Obesity is then split into three grades. The healthy weight BMI is associated with the lowest risk for chronic diseases in adults until 65 years. The overweight BMI has a slighly increased risk but the risk seems to depend more on the lifestyle and genetics. Risk is increased for the underweight and obese category. The higher the obesity grade the higher the risk for developing chronic diseases. Keep in mind that we are talking about risk. It is more likely that people in the obesity category develop chronic diseases, but there will be plenty of people with a higher weight who will go through life healthy.

A better way to determine the risk for chronic diseases is by body fat percent. Before we look into the methods to determine body fat we need to straighten out some terminology.

While the BMI sets the body weight in relationship to height it will not be able to tell us anything about the body composition. The body composition describes the relationship of fat mass to fat-free mass or lean body mass of our body.

• Fat mass is the amount of adipose tissue which is 79 % fat , 3 % protein and 18 % water.
• If we subtract the fat mass from the body weight we will get fat-free mass. Fat-free mass includes muscle, organs, blood, electrolytes, bone and body water.
• When it comes to future health he relationship between muscle and fat give us the best idea how healthy our body is. The best approximation is the lean body mass which includes muscle and organ tissue. Bone (mineral deposits) and extracellular fluids (blood and water outside of cells) are excluded.

Once we separate this out we also need to understand that there are different kinds of fat mass. Every body needs a minimum amount of fat to function properly. This is called the essential fat which is located within organs and tissues. The remaining fat is considered storge fat. It is located under the skin and around organs. As you learned in the lipid chapter, storage fat is important to cushion and insulate our body and organs.

A different way to categorize fat mass is to differentiate it by location in the body.

• Subcutaneous fat is located under the skin
• Visceral fat is located in the body cavity surrounding the organs.
• Ectopic fat is fat within muscles and organs.

High amounts of visceral fat are connected to an increased risk for chronic diseases such as T2D, CVD and non-alcoholic fatty liver disease. If people have less visceral and more subcutaneous fat their risk is much lower. As people gain weight and age they deposit more ectopic fat. While some ectopic fat is necessary for organ and muscle function, too much accumulation of ectopic fat impairs the function of the tissue. For example, accumulation of ectopic fat in the muscle reduces performance.

From studies looking into chronic disease risk we know that a body fat content of 21 – 35 % carries the lowest risk for women and for men that number is 8 – 24 %. You might have noticed that women have a higher goal. Women need this additional fat mass for reproductive function.

Body fat under 12 % for women and under 3 – 5 % for men is associated with fertility issues, reduced bone health, muscle wasting and an impaired immune system.

How do we determine body fat? Three methods determining fat mass are expensive laboratory methods used in research. The devices are prcise but expensive to buy and maintain. Densitometry (underwater weighing and air displacement) determine the body volume. Formulas allow the researchers to calculate body fat bringing body volume in relationship to body weight. DEXA (dual x-ray absorptiometry) is the most precise method and can determine not only fat mass but also lean body mass. You will see DEXA machines in hospitals to determine bone density and research labs. Bioelectrical impedance (I explain how it work for the next slide) can be found in research labs but less precise and less expensive devices can also be found in gyms.

The problem is that the devices determining body fat reliably and precisely are too expensive for physicians and not mobil for screening events. A more practical and portable method are calipers measuring skinfold thickness. A technician pulls the skin from the muscle usually on the upper arm, the scalpula (flat bone on your upper back) and the hip. The measurement of the skinfold including skin and subcutaneous fat can be entered into a formula yielding body fat percent. The issue with this method is that it will require a trained technician who understands how to precisely pull the skinfold. Otherwise the result will be unprecise.

Understanding the methods for fat mass determination it becomes clear that fat mass determination is not a practical screening tool to determine chronic disease risk.

Lately, a new device is on the market that has the potential to replace the BMI over time. Smart watches using bioelectric impedance to determine body composition. BIA (bioelectrical impedance analysis) devices send a weak electrical current through the body. Since fat with a low water content transmits the current slower than muscle mass with a high water content the device can calculate the body composition (fat mass and fat-free mass). Precise laboratory devices have large sensors sending the current through the entire body.

Smart watches use a smaller sensor sending the current through the upper body and back to the device. The question is how precise those smart trackers are. A few preliminary studies found that smart watches are similar to the larger gym BIA devices. These devices are reasonable precise for personal tracking of body composition over time to generate awareness and motivation. The precision is not sufficient for research though. Over time smart watches have the potential to replace the BMI.

Since we are on the topic of smart trackers. Studies show that using smart watches to track daily activity increases awareness and motivation. People using trackers increased physical activity by 60 %. While smart watch tracking works well to increase physical activity  studies also show that tracking does not work as well for improving eating or sleep habits.

When we determine if weight is healthy or not, the BMI can scan populations for following up. A better health indicator is body composition. In addition to body fat we also need to consider where the fat is located. Bodyweight located in the midsection is called central obesity having the appearance of an apple shaped body. Central obesity carries a higher risk for chronic diseases than a pear shaped body when adipose tissue is distributed around the hips and thighs. Additional subcutaneous fat carries a lower risk for chronic diseases than visceral fat.

Body fat distribution can be determine by measuring the waist circumference. Physicians should follow up with further assessment if women have a waist circumference over 35 inches and men over 40 inches.

In summary, what a healthy body weight is can vary from person to person. Healthy weight has multiple contributing factors. BMI can be a starting point as well as body composition and body fat distribution. Those measurements should be followed up by a physical and nutritional health exam, family history of obesity and chronic diseases and personal feelings about one’s body.

Ultimately, a healthy weight is a weight that supports optimal physical function and reduces our risk for chronic diseases, and a weight we feel happy about.

3. Weight Loss Is Possible, But the Maintenance Of the Lower Weight Is Extremely Difficult

The prevalence for obesity rose between 1999 and 2020 from 30.5 % to 42 % of the US population. During the same time severe obesity rose from 4.7 to 9.2 %. Despite the concerning rise in obesity and severe obesity, Americans try to lose weight. CDC data from 2018 show that 56 % of women and 42 % of men try to lose weight every year. The weight loss and weight management industry is flourishing and expected to grow from 224 Billion in 2021 to 405 Billion in 2030.

The reality of weight loss is frustrating. Only 20 % of people losing about 10 % of their weight maintain the lost weight at the end of the year. Looking at long-term weight loss maintenance the reality is even more sobering with the majority of people slowly gaining the weight back or even exceeding the starting weight.

Health care provider often chalked up this inability to maintain a healthy weight to a lack of discipline or just laziness. This is far from the physiological facts. During the next slides we will explore what happens during weight loss and maintenance.

Why Do so many People Gain Weight

First let’s explore why so many Americans gain weight in the first place. Energy balance is regulated by two systems.

The first system is metabolic, the homeostatic pathway. The center of the homeostatic system is the hypothalamus in the brain coordinating multiple inputs to increase or decrease the drive to eat:

• Endocrine signals from the gastrointestinal tract such as ghrelin secreted by the stomach signal hunger and satiation during a meal. The shrinking stomach hours after a meal triggers the secretion of the hormone ghrelin. The brain registers the increased ghrelin blood concentrations. We start feeling hungry. As the stomach fills and expands during a meal ghrelin secretion tapers off and satiation sets in.
• If we gain weight the growing adipose tissue increases the secretion of the hormone leptin. The hypothalamus detects those higher concentrations and reduces the drive to eat. If we lose the weight the opposite happens. Falling leptin concentrations increase the drive to eat.
• Increased energy expenditure due to physical activity or thyroid hormone secretion is registered as well and factored into the decision by the hypothalamus to increase or decrease the drive to eat.

If the energy balance was solely driven by the homeostatic pathway we would all effortlessly regulate our energy intake according to our energy balance. But, the regulation of the energy balance is complicated by the hedonic pathway.

The hedonic pathway has multiple cognitive and environmental inputs also registered by the hypothalamus in the brain. The problem is that the hedonic pathway operates subconsciously and we often do not even register how our environment drives our appetite and eating. Hundred of years ago when food shortages altered with times of food abundance the hedonic pathway was a survival tool. In times of food abundance the hedonic pathway overrides the homeostatic pathway triggering weight gain. For example, the hedonic pathway drove overeating and energy storage during summer and fall so people had enough energy reserves during winter and early spring.

Today, the hedonic pathway is in constant overdrive negating the homeostatic pathway. We are living in a food environment marked by an abundance of cheap, convenient, energy-dense food in large portions. Fast food chains, vending machine, fast, casual dining are available everywhere providing sweet, fatty and salty delicious food.

Daily physical activity is a thing of the past. We drive everywhere, spent our days sitting at a desk, communicating electronically. For every household or garden chore we have an electrical tool. Our spare time is spent relaxing, watching videos on our electronic devices.

How much we are effected by the obesogenic environment depends on our genes and or social and physical environment. For most Americans this means a slow weight gain from childhood to middle adulthood. More and more children are already obese and develop chronic disease in their teen years.

Once Weight Is Gained The Metabolism Works Hard To Hold On To the Higher Weight

Short-term weight loss is possible independent of the weight loss diet. Low-carbohydrate and keto diets tend to trigger a more rapid initial weight loss which is in part due to the loss of water from the clearing of glycogen stores and breakdown of tissue protein; both tissues contain around 75 % water. The rapid initial weight loss is not the most important part about weight loss strategies though.

Weight loss has three parts:

1. Fast weight loss during the first months
2. Slowing of the weight loss ending in a plateau
3. Slow, progressive regain of body weight starting around month 6 to 9

The majority of people will regain the lost weight over the next years often ending up with a higher weight. Research over the last decades identified some of the factors that lead to this weight regain (independent of the weight loss diet).

First there are the metabolic adaptions triggered by the weight loss. The total energy expenditure (TEE) will decline in average—this varies from person to person—20 – 30 kcal per day. Most of the reduction comes from a declining BMR. The metabolism becomes more efficient by secreting less thyroid hormones and increasing the parasympathetic nervous system. On the other side of the energy balance the drive to eat increases by increasing appetite. This is due to endocrine regulations. The adipose tissue secretes less leptin, increasing the drive to eat, and GI hormone secretion alters to increase hunger and reduce satiation during a meal.

Reduced TEE will make it necessary to eat even less to maintain the lost weight or lose more weight. Increased drive to eat makes it difficult to maintain the lower energy intake. In addition, the slowing weight loss impacts motivation. The cost of weight loss becomes higher compared to the benefit. In longer studies following weight loss with a low-carb or keto diet we clearly see that carbohydrate intake increases and the eating slowly reverts back to old habits.

Even worse, studies show that the reduced BMR, often 300 to 500 kcal less than expected, will persist for years after the weight is regained leading to further weight gain. If people go from one weight loss to weight regain to another weight loss diet, the BMR keeps decreasing.

Weight Loss Is Possible, Maintenance Of the Lower Weight Extremely Difficult

It is important to clearly state: People struggling to lose weight are not lazy and they do not lack discipline. Their metabolism works hard against the weight loss. Weight regain happens between the individuals biology (metabolic adaptions, genetics), the obesogenic environment (do we have education and skills to avoid marketing, temptations and convenience) and our behavior (for example stress eating, eating when bored, overeating).

We need to change how we think about weight loss. First, weight loss will require life-long management. Weight loss is not just about the initial weight loss phase but the focus should be about long-term weight loss management. Other factors impacting weight loss success emerge from studies.

• Mange your expectations: Wile most people expect a weight loss of 20 – 40 %—social media suggests even more drastic goals— weight loss of 5 – 10% shows consistently improved metabolic health. People should also be educated that the initial weight loss is achievable but only the start. Long-term weight management is difficult.
• Increase motivation: As we already discussed motivation will decline once weight loss is slowing or the weight loss plateau is reached. Motivation can still be increased by focusing on the overall progress and health improvement instead of the scale.
• Long-term support: Especially during the first year, ideally longer, people will need support by health care professionals in form of behavioral counseling and training and a support group.

When it comes to the dietary changes they need to be acceptable in the long-term. People should not expect to follow a weight loss diet for six months and then go back to their pre-weight loss eating habits. This means that extreme diets such as the keto diet or a low-carb diet are not well suited for weight loss despite their rapid initial weight loss.  These diets might be used as a starter diet but over the first half years eating needs to transition into a healthy, acceptable eating pattern that can be maintained life-long.

Higher protein intake (eat protein, not drink it) seems to improve satiety. Together with smaller frequent meals higher protein intake seems to be beneficial to curb the increased hunger and reduced satiation.

Self-monitoring leading to better self-awareness is a good tools. Together with behavioral tools such as having a contingency plan for situation when overeating is likely people will be better equipped to navigate our obesogenic environment. Given the high caloric, unhealthy, tasty and convenient food system, people managing their weight successfully tend to enjoy an occasional eating-out but cook the majority of their meals at home using fresh ingredients.

Overall there is a high degree of individuality—genetics only explain a small part—and people need to work out, hopefully with the help of a professional what works for them.

In addition, life needs to be restructured to implement other health behaviors. Sedentary time (screen time) should be reduced and replaced with physical activity. Regular exercise, both aerobic and strength training, will not trigger weight loss by itself, but helps to maintain lost weight and increases metabolic health. For example, increasing muscle mass will increase the BMR making up for some of the TEE reductions. In total people on a weight loss and maintenance journey should make space for 60 minutes of physical activity on most days.

4. Orthorexia: When Healthy Eating Becomes An Obesession

Monitoring your eating and eating a specific, restrictive diet has it’s risk. Over the last decades a new eating disorder has emerged: Orthorexia. So far orthorexia is not recognized by the DSM-5 the standard for classification of mental disorders used by mental health professionals because orthorexia is so new and not well researched enough to be included. What is it? Usually orthorexia starts out with good intentions of eating a healthier diet. At one point—we don’t know exactly what triggers it—healthy eating turns into an obsession. Suspects are the social media environment micromanaging eating and an existing tendency for restrictive eating.

The compulsive checking of ingredient lists and constant concerns about that food might damage one’s health has social and mental health consequences. Daily quality of life and social interactions decline. The person isolates more and more and mental health declines.

When food groups are eliminated and only a narrow range of foods are eaten, the person with orthorexia is at risk for nutrient deficiencies and malnutrition. The risk for anxiety and depression and other eating disorders increases.

Keep in mind there is a fine line between being passionate about healthy eating and being obsessed with it. On the right side of the infographic above, you will find a list of warning signs. If you suspect you or a friend and family members struggle with orthorexia contact UNL CAPS. or another counseling service if you are not an UNL students. A good start might be here.