[Food as Medicine] Food and weight

When is someone considered overweight?

The Body Mass Index (BMI) relationship between weight and height was originally developed in the early 1940s by Actuaries at the American based Metropolitan Life Insurance Company.

It was used to assess the risk of death, and therefore calculate life insurance premiums. Their data demonstrated that those with a heavier weight compared to their height were at greater risk of death (in particular from cardiovascular(심장혈관의) disease) than those with a lower weight compared to their height.

These BMI tables, albeit updated from the 1940’s, still remain one of the most widely accepted ways to assess risk to health from overweight by using simple anthropometric (body) measures.

Many people are familiar with the BMI as an indicator of whether an adult is of a healthy weight or not. BMI is based on the relationship between your body weight and your height and is calculated by dividing your body weight in kg by your height squared measured in metres:

BMI = body weight (kg) / height (m2)

The BMI concept relating weight to height, and its relationship with risk of mortality has now been verified in many long term studies. People with a high BMI in the obese range have been clearly shown to experience a much greater risk of mortality from all causes than people whose BMI is in the healthy range.

Risk increases as BMI increases. Hence, public health messages strive to encourage the population to keep their BMI within the healthy range.

Adult BMI ranges which describe ‘weight’ status

The following table provides the ‘cutoff’ values commonly used to describe overweight and obesity in adult caucasian populations.

Body Mass Index	<19.5	20 to 24.9	25 to 29.9	30 to <35	35 to 39.9	>40
(kg/m2)	Underweight	Healthy weight	Overweight	Obese Grade 1	Obese Grade 2	Obese Grade 3

Note: The term ‘morbidly obese’ is sometimes used to describe those with a BMI >40 kg/m2 who are considered at very high risk of illness or death due to their excess weight.

Known shortcomings

While BMI cutoffs are widely used, some shortcomings are known and should be highlighted:

• They are relevant only to adults. Children require different BMI cutoffs to assess their risk as do elderly people and those with chronic diseases.

• Different ‘cutoffs’ are also used for different ethnicities, for example, in Asian and Aboriginal people. This is due to differences in bone structure and differing levels of disease risk when overweight or obese.

• BMI is based only on body weight and does not distinguish(구별하다) between body muscle and body fat. So some individuals who are very muscular may have a BMI in the overweight range and yet have a normal level of disease risk.

• BMI does not distinguish where body fat is deposited. Risk is much higher when fat occurs around the abdomen

The importance of circumferences to estimate disease risk

Fat deposited around our central body zone is often the first thing people notice they are becoming overweight.

Evidence suggests that fat deposited on the abdomen increases health risks more than fat deposited on the legs, arms or hips.

For this reason, interest has grown in measuring waist and hip circumferences. This is easily done using a simple tape measure. Either the waist circumference alone or the ratio of waist circumference to hip circumference (distinguishing an ‘apple shape’ from a ‘pear shape’) are used to estimate health risks.

Different types of fat

As we now learn more about what factors increase our risk of disease and in particular the health issues around obesity, the role of different types of body fat has become clarified. In essence, our bodies have two different types of fat: subcutaneous fat (피하지방) and visceral fat (내장지방).

Visceral fat is laid down around our main organs in our abdomen, in particular around the liver, pancreas and kidneys. Once thought to be inert and not metabolically active, we now recognise that visceral fat produces inflammatory agents that drive metabolic disturbance.

Those people who tend to lay down fat around their abdomen (‘apple shape’) have more visceral fat and tend to have a greater risk of developing Type 2 diabetes, cardiovascular disease and stroke.

So, the measurement of waist circumference has become a useful and quick indicator of this disease risk.

What we know

More recently nutritionists have become interested in the ratio of Waist circumference to Height. Evidence shows that people with a high waist circumference compared to their height have a greater disease risk than people with a lower waist circumference compared to their height.

Unlike BMI, the same waist to height ratio cutoffs can be used with different ethnicities and they can also be used in children.

The useful take home message regarding waist-to-height is ‘keep your waist to half your height’.

Using risk indicators

All measures of health risk and overweight, are designed mainly to be used to examine risk for whole groups or populations. They are measures that are simple to perform and cheap to use on large numbers of people. But they are less good at estimating an individual’s actual level of risk.

To find out how much fat a person has on their body and exactly where this fat has been deposited we need to use much more complex methods that can tell us about body composition.

What lies beneath…

Our bodies are comprised of four different compartments which are: water, fat, lean tissue (muscle) and mineral (bone). There are gender differences in the amount of fat and lean (muscle) we have on our bodies, with males having a higher proportion of lean and a lower proportion of fat than most women.

Available technology

To measure these different compartments or our ‘body composition’ we need to use more sophisticated methods than a tape measure. A measure of body composition can be more informative for an individual than either BMI or a waist: height ratio as it can provide detail as to how much body fat they have and enable a more tailored approach to assess and perhaps reduce their risk of developing diabetes or cardiovascular disease.

One reference method for body composition is Dual Energy X-ray Absorptiometry (DXA) which gives an accurate measure of actual amount of fat, muscle and mineral (bone) that person has and also where it is located in their body.

Remember that the visceral fat located around the abdomen where the main body organs are located is the sort of fat that is particularly associated with the common chronic diseases that lead to premature death.

These scans can be helpful at an individual level to monitor the effectiveness of diet and or exercise on body fat and on lean or muscle. In weight loss, what we ideally want to achieve is a reduction in body fatness with preservation of lean or muscle mass.

Assessing body composition

If you’d like to learn more about the advantages of a body composition assessment, consider taking part in this activity.

1. ...who have the same BMI within the ‘normal range’ but very different body compositions.*

2.21 body composition scanes.pdf

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1. Examine the scans and then within the Comments, share with other learners which person you think is more likely to have the greater risk of cardiovascular disease.

2. Within the Comments, discuss if knowledge of their body composition could be helpful to these women and whether diet and or activity could be used to alter their %body fat.

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What factors affect a person’s weight?

Most people can tell you that if you want to lose weight you need to eat less food and do more exercise. This advice is quite correct, based on the principle that the body responds to its energy balance.

Diet and exercise and energy balance

Energy is taken into the body as food, and energy is lost in undertaking body functions and in movement and exercise. Any energy in excess of what is needed will be stored mainly as body fat. Any energy deficit will be made up by burning energy from body stores.

If the principle of energy balance is so simple, then why is it so hard for people to lose weight?

Many, many different factors can affect our energy balance. We can think about them under two headings: the inherited factors and the environmental factors.

Inherited(유전의) factors and body weight

Our genetic inheritance can affect how easily we gain or lose weight. All people are different. Some people will move around more than others and use up more energy. Some people absorb their food a little more efficiently than others. Some people have a stronger craving for fatty, sweet foods than others.

So even in societies where conditions make it hard to become overweight you will see people of different size and body shape due to these inherited differences.

Some people will be just a bit larger, some people will be just a bit smaller.

Environmental factors

In Westernised societies all over the world, people are now getting steadily more and more overweight. This change is happening very quickly. It has happened over just 20 or 30 years. This is much too fast to be explained by a change in our genes, so we must look for explanations in changes that have happened in our environment.

What are the triggers that are causing us to eat more and to exercise less? It is here that we can understand why it is so hard to lose weight.

Environmental factors and food intake

Energy intake is stimulated by the presence of food and by high food variety. Food in Westernised societies is now plentiful, affordable and always all around us. How many restaurants, food outlets and shops selling food do you see every day on your way to work or school? How many glossy advertisements for food would you see? How many appealing kinds of snack food are sold in your local supermarket?

A lot of the foods that are strongly advertised are energy dense foods - food (or drink) that supplies many calories in every gram, ounce or cup. Choosing energy dense foods makes it much easier to consume more energy than you really need so that you readily gain weight.

Technical advances in agricultural food production, food distribution and food manufacturing has made many foods that were once scarce –only eaten as special treats and at festive events-have now become very common and quite cheap. Foods such as chocolate, beef steak, ice-cream, sweet cookies and cakes, soda drinks, candy; these rich foods can now be eaten every day.

Food manufacturers have also learned that they can make more money from selling foods as large sized items rather than in smaller amounts.

Over the decades, the portion size of many ready-to-eat foods has increased considerable. This encourages over-eating as so many of us have grown up being told not to waste food and to eat up everything on our plate.

Healthy choices

Often people are told to just carefully select healthy food and they will lose weight. But how easy is it to do this? Have a look at your local supermarket. How many healthy foods do you see? How many are unhealthy? How many foods are loudly advertised as healthy choices when really they are high in calories? Now take a look at the places where people buy their lunch. What is the food choice like?

Very often you will find that the main foods for sale are not salads, fruit and whole grain breads and cereal products but energy dense chips and fried foods, pasta covered in cheese, rice dishes heavy with oil, sugary cakes and biscuits.

A food supply that does not emphasise healthy choices is one which makes it much harder for people to lose weight.

Weight loss and exercise

Weight loss is aided by an active lifestyle with regular exercise. But how easy is it for people to be active in Westernised societies? We often travel by car and do not walk far. Even if we want to walk or cycle there may not be any walking tracks, good pavements (sidewalks) or bicycle paths that are safe and away from the traffic. You may not feel safe out walking when it is getting dark. You may think walking is a good idea, but you have no time to fit it into your busy work day.

For many of us, work or at school involves long periods sitting often looking at a screen. We are very busy but we are very inactive(활동하지않는). Our opportunities for relaxation then often involve even more sitting- watching TV or another kind of screen.

In addition, many of the domestic tasks that used to require labour have now been mechanised. We have dishwashers, washing machines, vacuum-cleaners, lawn mowers, electric hedge clippers- even TV remote controls.

Our everyday environment no long requires us to exert much energy.

Environmental change

So when you think about our food environment and our physical environment you can see that there are many factors acting on us that make it difficult to lose weight - and instead are causing many people to continually gain weight.

Some people are more influenced by one factor than other. For one person the problem will be that they spend far too much time sitting, for another person it will be the choice of three jam doughnuts as an afternoon snack. So to change outcomes for populations as a whole, many different things need to be addressed.

In the future, public health workers hope that these many environmental factors impacting on our body weight can be improved.

We need to think about how to change our food supply and how to change our built environment in cities and towns, how to change our habits and entertainment, so that it becomes much easier for people to have a healthy lifestyle and control their body weight.

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Weight regain: why does this happen so often?

Helen Truby : video transcript

One of the issues that people face when they lose weight is the problem of actually keeping it off. So although we know how people can lose weight-- and a lot of people are very successful at that-- the majority of people do experience weight rebound. And over two or three years after losing a substantial amount of weight, unfortunately, the majority of people will regain it. So this is obviously quite depressing for people and is not a great outcome for them.

So there has been quite a lot of work done on the reasons why people regain weight. And some of it's about our physiology, that our bodies defend a set point in our weight. So in other words, it decides what weight you're going to be and then it actively defends that position. So if you lose weight, it tries to get you back to where you were. And it's a combination of your brain and your gut. So your gut hormones send signals to your brain telling you that you're more hungry and that you want to eat more. So consequently, obviously if you in a reduced weight state, if you eat more, you're going to start gradually gaining that weight back on.

So it is hard for people to actually maintain lost weight. But we can learn things from people who are successful at this. And we've learned from people who have lost weight and maintained weight loss for more than a year. And we know certain things, they have certain characteristics. So these characteristics are one, they self monitor their weight regularly. So in other words, they'll weight themselves at least once a week, maybe twice a week. And if they've gained a little bit of weight, they're active about losing that weight again, so they don't get that weight creeping upwards. Two, they're reasonably active. It's not major amounts of physical activity, but it's basically walking. And people need to do at least half an hour to an hour a day, of trying to maintain a physical activity level. The other things, in terms of diet, that successful weight loss maintainers do is that they eat breakfast, they tend to eat regular meals, and they tend to have the same food. So in other words, people get into a bit of a pattern and a bit of a rhythm about this is what I have for breakfast, this is what I have for my morning snack, this is what I have for lunch. And people's evening meal might vary a bit, but the amount and quantity of food that they eat doesn't vary too much. So those seem to be some tips that really help people be successful in maintaining weight lost.

So this theory of set point weight would seem to indicate that people find it difficult to reset that weight point. And once people have become obese, it's really difficult for them to actually maintain a lower weight. So it's not necessarily because people don't try. It's that physiologically it's very difficult for them. And I think we need to recognize that more in society, about how hard it is for people to actually maintain weight lost. It's not impossible, but it's certainly quite difficult for people to do.

So one of the reasons why we're moving more towards prevention of weight gain is that, obviously, if you don't reach that obese state, then it's easier for you to have a physiological set point that's lower. So there are key times in our lives when we know people are more susceptible to weight gain. And in women, it's particularly around pregnancy and between pregnancies. So people gain weight when they're pregnant. Obviously then they lose weight, hopefully, during breastfeeding times and when their babies are small. If they don't go back to their original weight and they get pregnant again, that tends to be a period of time where people will continue to gain weight. And it's very hard. So there are key times when people perhaps can be more sensitive about trying to reduce their weight back to what it was before they were pregnant, before they have another baby. So those strategies might help certain groups of people, but it is difficult, and it's not something that we entirely understand about how we might be able to reset people's point for weight. It's not impossible, but it's certainly challenging for most people.

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Is dieting the answer?

Helen Truby : video transcript

An adult's energy balance works by simply, the arithmetic between energy in and energy out. So energy that we have from our food and our drink is obviously energy in. That needs to balance the amount of energy we're actually expending in activity. So our bodies also use a basic amount of energy every day.

There are numerous studies around that have tested various different diets, and the answer is they all perform reasonably well. The challenging aspect is ensuring that you can maintain that dietary pattern over a period of time, so you can keep that lost weight off.

Recent popularity in terms of diets has been modified fasting. So in other words, not eating on certain times of the day, or whatever. And again, if that's a mechanism whereby people find that they can manage their weight, then well and good. The only issue is around diet quality-- in other words, nutrient density. So if you're going to skip a couple of meals twice a week or three times a week, you need to make sure that you're going to get your micronutrients that you need that you're going to miss out on, simply by not eating later on in your diet-- particularly important for women, in our iron requirements. Particularly important for women of childbearing age as well, if you're planning a pregnancy. So there are elements of lifestyle as well that's important. And picking something that you're going to be able to stick to. But in all honesty, most of them will work for you as long as you reduce your overall energy intake. You will lose weight. That's physiologically the way it sits.

So activity, whether it comes in the form of walking, standing, running, anything like that, it's going to burn energy. So that adds to our energy out equation. And one of the issues that we have largely in our society now is that people are very sedentary (앉아서 행동하는). So we don't do a lot of physical activity everyday. And the more sedentary we are, really the less energy we actually need to have. Because we simply don't burn up enough energy.

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Feedback from the course educators

https://youtu.be/emKflE6shAI

 

2.29 Feedback from the course educators.pdf

0.07MB

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• ⁃ Reference 

Food as Medicine from Future Learn. free courses https://www.futurelearn.com/courses/food-as-medicine

Food As Medicine Online Nutrition Course - FutureLearn

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