Weight management and obesity measurement

We will talk first about BMI (body mass index), which can be calculated dividing weight in kg by height in meters squared. If i have 84 kg and 1.78 m, then my BMI will be 84/(1.78 x 1.78) = 26.51. Between 20-25 you are good, 25-30 overweight, 30-40 obese, over 40 morbidly obese. The only problem is that this method will not take in account your body composition, so if you are an athlete with well developed muscles, according to this method you can be classified overweight. BMI disregards the body fat distribution, which can be useful to show heart risks.

Other more accurate method is the Fatfold or Skinfold method. This one measure the thickness of the skin (including the underlying subcutaneous fat layer) using a Skinfold caliper. We measure front tight, upper back, waist and upper arm. There is a strong correlation between the thickness of the subcutaneous fat layer and the total amount of the body fat.

There are some exotic techniques such as Hydrodensiometry (underwater weighting) and Air Displacement Plethysmography, which both measure the density of the body, dividing body mass by body volume. Body density can be used to compute body fat percentage using a mathematical formula (assuming fat density is 0.9 and lean body mass is 1.1 as constants). The idea behind this is that obese people with low body density will float in water and lean people with high body density will sink more in water.

Other way is by using Bio-electrical Impedance, sending tiny electrical impulses through the body and measuring the return of impulses, as lean tissue conducts electrical impulses more easily than fat tissue. This method is now affordable, easy to use, but not very accurate.

DEXA (Dual Engage X-ray Absorptiometry) is a method that uses x-ray to determine body composition (including details like done density). It is very accurate, very expensive and has small risks due to irradiation.

Non-obese males value is 10-20% body fat, non-obese females 20-30% body fat. As we age the body fat increases as we replace muscle with fat.

Protein quality and recommendations

For optimal synthesis of body protein, all the aminoacids need to be present in adequate quantities and proper proportions. Any essential aminoacid deficit will drastically limit the synthesis of much needed protein.

You need to learn about the concept of limiting protein. The limiting protein is the least abundant aminoacid in a dietary protein source (for example for wheat the limiting protein is the lysine). By combining different dietary protein sources you will provide with a wide array of aminoacids.

Protein quality has two variables. First is the digestibility (what percent of the dietary protein is absorbed into the body), second being the aminoacids composition (the higher the similarity of aminoacids composition and the average body protein, the higher is the quality, so, obviously, animal proteins are better than plant proteins, unless you combine various sources). A meal or a diet should have a mixture of different  proteins. A mixture of plant-based proteins will have a more favorable aminoacids composition than one individual plant. This is called protein complementation - combining more proteins to achieve higher protein quality (grains are low in lysine, and beans are low in methionine, but together they are well balanced).

Methods to measure protein quality:

1. Biological value (BV) - measure of the protein percentage absorbed from a food to be incorporated into the body.

2. Protein efficiency ratio (PER) - weight gain divided by its intake of a particular protein during test period. PER was the official method before getting replaced by PDCAAS (protein digestibility corected aminoacid score). AAS (aminoacid score) is calculated for any particular protein comparing the level of limitating aminoacid in the protein towards the level of the same aminoacid in a reference protein. PDCAAS for milk is 1, for isolated soy protein is 1, for wheat is 0.4, for beans is 0.6-0.7, but wheat combined with beans is almost 1. PDCAAS is easy to calculate , based on the human aminoacids requirements.

DIAAS (digestible indispensable aminoacid score) - the diference is that, while for PDCAAS indigestability of a particular protein is measured in stool, for DIAAS is measured in terminal ileum, being more accurate.

The recommended protein intake is 0.8 grams per kilogram weight (56grams for a 70kg adult). Most people have more than RDA (required daily ammount), as protein is 10-25% of our total energy intake. You will have above 20% if you eat mostly meat, eggs and dairy. Endurance and strenght athletes eat 1.2-1.7 grams per kilogram (and many do not know that you can achieve this through diet alone, without any supplementation). According to the Journal Of Sport Sciences, it is ideal to consume them as soon after exercise, for them to be optimally used.

Beware: even if it is unproven, there are some potential health effects of protein that are promoted by media.

- High protein intake to be avoided by patients with kidney disease.
-No conclusive evidence to link proteins to cardiovascular diseases, cancer or osteoporosis.
-No conclusive evidence that there is a relation between protein intake, energy intake and body-weight.
-Between animal and plant-based proteins, the animal food is bad because of the package (more fats, salt and carbs), not because the proteins from the aminal sources are bad.

Next posts will be about energy requirements and energy balance. Have a wonderful day!
G.