PLT4M’s nutrition education series has tackled a wide variety of subjects like macronutrients, micronutrients, and types and timing of meals. In our more advanced series “Applied Nutrition,” we take on the topic of weight. Rebecca Toutant helps students to understand and start to define the major differences between weight and health.
We live in a world where body weight and size take center stage in many discussions, including health and performance. But these conversations often gloss over the actual research behind weight change. Body size cannot be controlled as easily as the world makes it seem. Furthermore, sometimes trying to be a certain weight or body size gets you farther from health instead of closer to it.
Weight, in particular body fat, is often the focus when it comes to health. There’s an idea that if a person weighs more than they “should,” they will have an increased risk of a wide variety of chronic conditions such as diabetes and heart disease. That’s because it’s assumed that someone who weighs more will have more body fat. It gives the impression that if size is “controlled,” body fat is controlled. And in turn, a person is protected from health problems.
This association of ideas creates the perception that those who develop a disease have “done it to themselves” for “failing to control their size.” But it’s not the complete picture. People in bodies of all shapes and sizes develop chronic health conditions. And there’s interesting evidence that other factors are more powerful than size alone.
To begin to understand the challenge, we have to explore how our world categorizes body size. From there, we can start to understand how there might be room for more flexibility in how we look at bodies and health. This is where we will set out on the topic of weight and overall wellness.
Author’s Note From Rebecca Toutant, PLT4M Nutrition Expert | MA, RD, LDN, CDCES, cPT
It feels important to share that I initially chose and shaped my career as a dietitian and personal trainer based on an intense interest in weight management.. Like many who join the field, I was driven by my own experiences and desire to help others. But as I did more work with people and furthered my education, I became aware of the limitations and potential harm that can come from “treating weight” without considering the person inside the body.
You may have your own experiences managing your own weight. You may also be heavily involved in the research around weight management. But as you read this, it’s worth remembering that helping people in a client centered, evidence based way, is about understanding the research in the context of the human experience. And that comes not only from working with a large number of people from diverse backgrounds but also considering the preference, experience, and needs of the person in front of you.
At this point, we have developed and worked through a variety of nutrition topics. Now it is time we tackle weight and all the intricacies of the subject. Let’s navigate this together and with a willingness to learn.
Check out the full “Getting Real About Weight” lessons and all of PLT4M’s Nutrition Content!
What Is Our Weight Made Of?
When we talk about weight, we often refer to the number we see when we step on a scale. This simple measure accounts for every cell in your body. This total number includes bones, muscles, organs, fluid, and body fat, to name a few.
Our weight is never the same. It changes hour to hour and day to day. In fact, most people fluctuate within a 5-8 pound range depending on when they step on the scale. Most people are lighter in the morning and heavier in the evening. These changes have nothing to do with our body fat. Instead, when you eat and drink, you add “weight” from the food and liquid. Your body uses some of that as energy, the waste will be removed as urine and fecal matter when you go to the bathroom, and sweating results in loss of fluid – all of which result in weight changes.
What Is The Quick Change?
Weight can change quickly, but body fat and muscle mass cannot. When you see quick changes on the scale, it’s almost always due to changes in the amount of water our body holds that come from sweating, urination, or changes in nutrients. As we learned in the hydration lesson, our bodies are upwards of 65% water. When we sweat and/or urinate, we lose fluid from the body, so the number we see on the scale will decrease.
But that change has nothing to do with body fat. When we drink fluids, the number will go back up. That’s because water has mass to it which creates a gravitational pull known as weight. Don’t believe it? Put a bottle of water on the scale. See how much it weighs.
Our weight may also change based on the types of nutrients that we eat. When our body is given more sodium (found in salt), our cells will hold more water to maintain fluid balance. If our bodies didn’t do that, we’d be in a lot of trouble. The retention of water actually increases our hydration. Many endurance and hot weather athletes will intentionally have more salt the day before and during big events or training to improve their performance. But exercise (or rather sweating) can also change weight quickly. Too often, people will do a tough workout and then step on the scale seeing their weight is down. It’s important to note this is NOT a measure of energy or body fat lost – this is purely the amount of fluid lost by sweating. Some folks may notice that their weight is higher after a workout. Sometimes this is due to drinking more water than needed, and other times it’s related to hormonal changes that come along with muscle repair.
But sodium isn’t the only nutrient that changes body weight. Another example is how our body stores glucose as glycogen. Remember from our carbohydrate lessons, our muscles and brain use glucose to function. So the body has a back up of glucose in the form of glycogen. The body contains about 500 grams of stored glucose (aka glycogen). Every gram of glycogen contains 3 grams of water. When people stop eating carbohydrates and/or use up all their available glucose, they start using glycogen. But with every gram of glycogen used, the body also removes 3 grams of water. Long story short, that’s why diets that restrict carbohydrates such as starches and sugar (like keto, Atkins, and paleo) lead to rapid weight changes. Most of the weight changes come from losing water – not body fat. That’s also why when you eat carbohydrates again (because your body needs them to optimally function), you may see the scale increase quickly. It has nothing to do with fat – just water.
Growth & Development
It’s also important to consider that weight increases are natural and normal, especially with growth and development. When we look at a body, it’s made of two categories of tissues that we often refer to as body composition:
69-82% of the body is lean mass, including muscle, skin, bones, and organs. And within these systems are fluid in the form of blood and fluid within cells.
18-30+% of the body is fat mass (also called body fat or adipose).
Before puberty, boys and girls have similar amounts of body fat. But right before puberty happens, both boys and girls will gain weight quickly (usually in the form of body fat) as the body prepares to increase in height and development. The extra energy stored as body fat ultimately supports muscles, bones, organs, and the reproductive system. If energy is restricted during growth and development, it’s been shown to reduce someone’s physical and cognitive growth potential.
It’s during and after puberty that body composition differs between boys and girls. Females tend to have (and need) a higher body fat percentage because the energy and nutrients stored in the body fat are essential to support the incredible ability to create, protect, and feed a baby. In contrast, males are more likely to develop muscle mass related to testosterone production.
While many people have a big height increase in puberty, most humans continue to grow and develop until their early 20s. As the body develops, body mass increases. As bones lengthen and muscles strengthen, they have more mass or weight attached to them. With growth comes more skin, which adds to our weight. As organs mature, they will have more weight as well. It may seem frightening, but it’s unrealistic and arguably unhealthy to try to maintain your junior high or high school weight – it’s not your adult weight. It can compromise your muscle and bone development to try to stick to a number from your youth.
It’s important to realize that the scale alone does not tell us what we are made of. Two people of the same height and weight can have completely different ratios of lean tissue and fat tissue because there is variation in how much muscle a person has and their bone and organ tissues. So if the scale doesn’t tell us much about our health… can body composition?
Exploring body composition
Often when people are attempting to change weight, what they’re really hoping to control is the amount of body fat they have. While body fat may seem “optional” or a nuisance, it is actually essential for health:
It provides insulation and temperature control.
It provides structure in every cell. It even provides structure and fullness to the skin.
It helps protect vital organs against injury by acting as a cushion. It also keeps organs stable and secure in the body.
It is where vitamins A, D, E, and K are stored in the body.
It provides a stored form of energy that we use during low-intensity activities. It’s also a source of energy when the body cannot eat, such as during famine or illness.
Body fat supports many hormones in the body, such as hormones that support hunger/fullness, the immune system, reproduction, and other regulating processing. For women during menopause, it also helps compensate for some of the negative impacts of estrogen depletion.
Fat tissue plays important roles in immune function. It communicates the body’s metabolic state to the immune system via hormones called adipokines, which control immune cell activity.
This is usually when people ask, “Well, what is the right amount of body fat for me?”
Evidence to date has identified most adult men need at least 3% of fat, and most adult women need at least 12% body fat for basic survival (children and adolescents need more but are not defined). And more commonly, “healthy” body fat percentages are 15-20% for males and 24-30% for females.
Please keep in mind that “minimums” are not goals; they are the least amount required to survive, not thrive. This means being at the low end of body fat percentage is not necessarily healthy, especially if it’s achieved by undereating. And that the higher end of the spectrum is also not the “most” someone “should” have. There is a great deal of individual variance in body fat percentages based on genetics and previous experiences with undereating and starvation.
You might argue that there are athletes, celebrities, and social media influencers with lower body fat percentages. And yes, some people naturally have lower body fat percentages. And others are able to dip below these thresholds for short periods. But evidence shows that trying to maintain ultra-low body fat percentages can have serious health consequences, especially if it is not within the person’s genetic design.
Body composition assessments and interpretations
It’s natural to be curious about what you’re made of. But unfortunately, it’s not an easy measure to actually get.
The most accurate body composition testing includes DEXA scans, Bod Pod, and underwater weighing. But these are expensive and typically only available through universities and research centers.
You may also be aware of some scales and handheld devices that promise to tell you your body fat percentage. But these are not very accurate by design and are known to be off by 3-11% (which is a very big window of error). Skin calipers are another option and may give a decent picture of body fat percentage depending on the person’s skill level taking the assessment.
More importantly, it’s crucial to ask yourself what is the value in having the assessment done. Truly, the most important reason to have a test done is with the guidance and supervision of a professional who has a deep understanding of health.
For example, having an accurate understanding of someone’s body composition can provide more accurate nutrition counseling and planning. But beyond that, measures like these often only cause people to feel bad about their bodies because they have unrealistic expectations of what their bodies should be made of.
And as we’ll learn in future lessons, trying to achieve a body fat percentage that is too low has many health consequences.
The most common “measure” people will turn to is BMI or “Body Mass Index.” It’s a simple equation that compares your weight in kilograms divided by meters squared (or BMI = kg/m2). It is essentially your body’s “density.” It does NOT tell you your body fat percentage. It does not tell you anything about your lean vs. fat mass.
It’s merely the relationship between your weight and your height. The number that you get can be used to compare yourself to a chart that determines what is and is not “normal.” And that chart and definition of “normal” was developed over 200 years ago by an astronomer, mathematician, statistician, and sociologist trying to “characterize the average man.”
Basically, he measured a bunch of mostly European men to describe the average weight to height distribution. Most of them fell between 18.5 to 25. Some were higher and some were lower. It was not originally designed to predict or determine the relationship between their size and health status. It was to describe the average size density at the time. It wasn’t until the early 19th century that there was a need for insurance companies to define risk, that it was applied to predictions about health.
Many studies and experts over the years expressed frustration over the limitations of the BMI, including…
It doesn’t tell you what you are made of. Your weight could be higher than average for your height because of more bone, muscle, and/or tissue.
It doesn’t account for biological differences in body composition. Women and many other racial groups were not included in the statistics.
It doesn’t speak to age differences.
It doesn’t tell you anything about how the person lives.
It creates weight bias and stigma.
Despite its many known limitations, many systems continue to use BMI as a way to define and assign disease risk to certain body types because it remains an easy and inexpensive way to make assumptions about bodies. But it’s really worth considering whether or not that number should “define” someone vs simply be a reference point.
It’s important to also know that the simple BMI calculation is not actually used for people under the age of 20. Because as we’ve discussed earlier, body composition is very different in someone who is not fully developed. Instead, after BMI is calculated for children and teens, it is expressed as a percentile. There is a different chart for boys and girls. These percentiles express a child’s BMI relative to US children who participated in national surveys from 1963-65 to 1988-94 (so again, limitations to its usefulness). Long story short, BMI is not interpreted the same way in children as adults. The BMI percentiles for children are relative to other children of the same sex and age from about 30-60 years ago.
What’s the relationship between BMI and health?
While the theory is that increased BMI may lead to increased disease risk, the research behind that is not consistent. Because people with “normal” BMIs can still have increased risk depending on their lifestyle and circumstance. And people with higher BMIs are not guaranteed to have poor health. What the research shows is that having a healthy lifestyle (eg, managing stress, sleeping well, eating well, staying active) can be more important than weight status. And this has shown to be true for those with an “elevated” BMI between 25-35. There may be a greater risk of health conditions as BMI goes over 35 as movement can become more difficult. But even then, very modest reductions of 5-10% of starting weight have been shown to reduce risk. It really debunks the idea that there’s a “right” and “wrong” weight to be.
Additionally, it’s worth knowing that the presence of body fat alone does not necessarily increase the risk of someone developing health problems. Where and how someone stores body fat can have an impact. For example, those who carry their body fat around their organs (known as visceral body fat) can change how those organs function. Those that carry their fat subcutaneously or just under the skin (usually around their hips, thighs, and arms) tend to have less of a cause for concern. But you can’t choose where and how your body stores body fat. This is largely determined by genetics but can be slightly changed with physical activity and managing stress.