Human Nutrition

2018-03-10 23:34:30 Jimbin Mai, Ph.D. 29


We all want to eat healthy, active and live long. Nothing wrong with that.  However, in order to treat ourselves right, we need to learn some basic about human nutrition.  There are specific nutrition required by the pregnant women, lactating mother, growing youngster, athlete, and aged population. We will talk about nutrition in general.  For those who are interested in specific nutrition, I suggest that you consult with licensed dietician.


Macro- and Micro-Nutrients

When dealing with nutrients, we divide it into both macro- and micro-nutrients.  In today’s discussion, we will only touch upon macro-nutrients, namely, protein, carbohydrates including dietary fiber, and lipids.



In general WHO recommends the use of PDCAAS (protein digestion corrected amino acid score) and now in the future DIAAS (digestible indispensable amino acid score) as a marker for protein quality.  The perfect score for either one is 1.0.  The reference proteins are in general egg white or casein.  I know of no plant protein has been used as a reference protein.  This is may be the reason in general that good proteins are biased to animal instead of plant protein!

When talking about protein, allergenicity is a sensitive word often been mentioned.  Egg, milk, soy, peanut and wheat gluten are of higher allergenicity while rice and pea are considered as of lower allergenicity. That is why now on the market place there are a lot of gluten-free products are being promoted. Pea protein based plant milk are now getting very popular.

Proteins are needed for muscle generation and repair, connective tissues and internal organ growth and repairs as well as they are important sources for enzymes which are indispensable for digestion and other important physiological function such as energy production.

Surplus dietary proteins would not be stored but excreted through kidney.

You might ask how much protein intake per day.  Good question! It really vary with the age groups.  Growing youngesters, pregnant ladies, lactating mothers, patients recovered from illness, and the elderlies all have different requirements.  In general, it varies from 0.8g to 1.6g/kg/day.


Carbohydrates can be divided as simple and complex carbohydrates.  Sugar and glucose are simple carbohydrates while starch and fibers are complex carbohydrates.  Nowadays, complex carbohydrates are being promoted while simple carbohydrates are been suppressed.  There are around the world proposal of sugar taxes and usage levels being limited in certain categories of products like soft drinks.  Glycemic index is being used as a measure as the speed of carbohydrates been converted into simple sugar after ingestion.  High glycemic indices foods are in general less desirable than the low glycemic foods.  For example, potato, white bread, and  white rice are considered as high glycemic foods while brown rice and multi-grain bread are considered as low glycemic foods.


Lipids includes fats and oils.  In general, fasts are less fluidic than oils at ambient temperature.  In another words, fats are more saturated and oils are more unsaturated.  Dietary recommendations are of both mono- and polyunsaturated oils over saturated fats.  

Of them, most mentioned are omega-6 and omega-3 oils on human nutrition and physiological functions.  There is a suggestion that the ratio of omega-6 and omega-3 oils needs to be at around 4:1 to be healthy.  However, due to agriculture and farming practice, the dietary intakes of fats and oils tend to be in favor of the omega-6 category and therefore nowadays that our ratio tends to fall into the 20-30 to 1 categories, which is geared to in favor of the inflammation-prone condition for our body.  Through dietary lipid manipulation, we need to try to correct the ratio back to the 4:1 ratio of omega-6 to omega-3.

The other subject on the dietary is the partially hydrogenated soybean oil (PHS), which contains trans-fatty acids and has been proved to cause coronary heart disease.  It took more than 30 years since its studies and reports on the deleterious effect to heart health and finally FDA put its foot down to ban the use of PHS in processing foods and cooking oils.  In turn healthier vegetable oil like high oleic Canola, safflower, sun flower and soybean oil is now available in the market place.  Of course I know that you are going to ask if these oils are GMO (genetically modified organism).  Let’s leave this subject out for the time being.


So, now you have some idea on the macro-nutrients required by us human beings.  On the next series, we are going to touch on the subject of animal vs. vegetable proteins.

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