Know the definition of obesity
Obesity is defined as being 20% overweight. Being obese increases the risk of many other conditions, such as type 2 diabetes, sleep apnoea and cardiovascular disease.
Be able to describe BMI
BMI, or Body Mass Index, is a simple method used to estimate the amount of body fat. It can be calculated by taking a person's mass in kg and dividing it by their height (in m) squared (i.e. BMI = (mass(kg))/(height(m))^2).
Know the limitations of BMI
One of the limitations of BMI is that it only takes height and weight into account. It also cannot distinguish between muscle mass and body fat. Hence, bodybuilders may be classified as overweight or even obese under the BMI system, despite having very little fat. Alternatively, people who have lost a lot of muscle may be classed as underweight, despite still having a decent amount of fat.
Know the WHO guidelines for BMI
- Underweight: <18.5
- Normal: 18.5-24.9
- Overweight: 25-29.9
- Obese: 30-39.9
- Extreme Obesity: 40+
Know why waist circumference is used when assessing disease risk
Since BMI, as I mentioned above, is imperfect, waist circumference is also used as a kind of "backup" measure. If someone is obese and has a large waistline, they are at a higher disease risk than someone who only has one of those factors.
Know some of the risk factors associated with obesity
As mentioned earlier, obesity can increase the risk of a variety of other conditions, such as type 2 diabetes, hypertension, other cardiovascular problems, and so on.
Be able to describe how changes in energy balance can lead to obesity
Obesity occurs when the amount of energy consumed is greater than the amount of energy expended. As excess energy is generally stored as fat, over a long time this can lead to the accumulation of fat and thus obesity.
Be able to discuss factors leading to obesity
Obesity can result from an overconsumption of food or a lack of energy expenditure. The former can result from eating foods that are too energy dense (see here for a definition of energy density) or increased appetite. Increased appetite also has a variety of potential causes, from genetic predispositions to psychological issues. Energy expenditure might be low if someone doesn't exercise regularly, and/or their NEAT is low.
Be aware of the current levels of obesity in Australia
They're not good- let's just put it that way. In 2012 56% of women and 70% of men over the age of 18 were overweight or obese. Also I remember one of my primary school teachers saying that we were beating the US in terms of obesity, but I can't find a source for that.
Be able to discuss the two misconceptions about obesity
One of the misconceptions about obesity is that it is caused by high fat diets. This isn't true as any macronutrient can be converted into fat, as I will explain shortly.
Another misconception about obesity is that obese people are more likely to have a low BMR, and vice versa. This is also untrue. Obese people have more fat, and all of that fat contributes towards the BMR. Hence, obese people often have a higher BMR.
Know that protein and carbohydrate can be converted to triacylglycerols
Both glucose (from carbohydrates) and amino acids (from proteins) can be converted to Acetyl-CoA, which can then be converted to fatty acids and then into triacylglycerols.
Be able to discuss how weight loss can be achieved.
There are drugs and surgical techniques that can help with weight loss. I've covered surgical interventions here, so let's talk about drugs. Amphetamines were one of the earlier drugs that helped with weight loss due to the way that they suppress appetite, but they can be very addictive. Another drug that is no longer in use for this purpose is sibutramine, which also suppresses appetite, but only for a short time until tolerance occurs. Furthermore, sibutramine can increase blood pressure, making it dangerous. A third drug that can cause weight loss is orlistat, which inhibits lipases in the GI tract and thus reduces the uptake of fats. Unfortunately, this causes unpleasant side effects, as well as deficiencies in lipid-soluble vitamins.
Thankfully, there's another way to achieve weight loss, and it mainly involves taking in fewer calories that you expend. This is easier to do by controlling your diet than exercising more, as unfortunately exercise doesn't really burn that many calories. That's not to say that exercise is useless, however: it's still good for building muscle as well as for general health and wellbeing.
Only two more lectures for this module! They're going to be on weight loss and exercise metabolism, so stay tuned!
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