Food Chemistry Basics: Proteins, Fats, and Carbs (part 6) - Protein - Eating Protein

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6.2 Essential Amino Acids

Proteins are composed of any of 20 amino acids, 10 of which are considered essential because they have to be obtained in your diet. The body cannot synthesize its necessary proteins if these 10 amino acids do not show up in adequate amounts in your diet: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine, as well as arginine (for infants) and histidine (for infants) (from Human Anatomy & Physiology, by Elaine Marieb and Katja Hoehn).


Exercise Physiology, by William McArdle et al., lists only eight amino acids as “essential,” and points out that infants cannot synthesize histidine and children have “a reduced capability for synthesizing arginine.”

The rest of the 20 amino acids are: alanine, asparagine, aspartic acid, cysteine, glycine, glutamic acid, glutamine, proline, serine, and tyrosine.

6.3 Eating Protein

When you eat protein-containing foods such as meats, fish, eggs, cheese, nuts, and plant foods, as we mentioned, proteases and other enzymes split up the big block of Legos into their separate amino acids, which can then be absorbed in the small intestine and released to the liver and bloodstream.

The body can do a number of things with these amino acids, depending on your physical needs:

  • The cells can take them up and use them as raw ingredients for proteins.

  • The liver can make glucose out of them for energy purposes, in a process called gluconeogenesis.

  • They can also be stored, after conversion by the liver to glucose or lipids, as glycogen (i.e., muscle fuel) or fat.


Yes, both excess carbs and excess protein in the diet can be stored as excess fat.

Proteins that are already in the cells (not coming in as part of your food) are constantly being degraded or split up into their constituent amino acids and resynthesized into new proteins the body needs. It’s a very complicated and ingenious metabolic process by which the liver finds so many different uses for proteins and amino acids, but one of the important elements of the sequence is that when the liver has to metabolize amino acids (in order to make glucose out of them, for example), the organ breaks down the amino acids into ammonia, which is converted to urea and excreted out via the kidneys in the urine.


Ammonia is toxic when it builds up in the blood, which makes the excretion of urea throughout the day so important. The rate at which this conversion takes place in the liver is limited, which is why the body cannot tolerate unlimited amounts of protein, as in “rabbit starvation syndrome.”18

Cells can take up the amino acids for their own use, such as new protein synthesis by muscle cells.


An iPhone and Android app exists for amino acid aficionados, appropriately called Amino Acid Reference.

If you aim for optimal health, you need to get all of the essential amino acids in high enough quantities from your diet. Meat and fish eaters have an easier time of it than vegetarians, for instance, because these meat constituents are generally complete proteins—they have all of the essential amino acids in greater than trace amounts. Eggs are a great source of essential amino acids for vegetarians (eat copious amounts of pastured eggs), as is the occasional whey protein shake .

Fermented Soy as a Small Protein Source

Ever tried tempeh, miso, or natto? If you’re Asian, Indonesian, or a vegetarian/vegan, your answer will probably be “Yes.” These are fermented soy products: the first originated in Indonesia, and the last two are well-known Japanese foods. They are part of a long lineage of traditional Eastern foods that consist of soy-based protein that is fermented; this removes most of soy’s nasty antinutrients, which prevent the absorption of minerals and protein . Natto’s a really good source of vitamin K. These are also decent soy-based protein sources, albeit in small amounts.

You get the protein, without the meat fats, if you so desire. I’ve been adding tempeh to my salads, and liking it. It has the consistency of a softer cheese, and tastes a bit like bland meat. It’ll soak up sauces and dressing if you add it to salads or soups (miso is often made into a soup, such as at Japanese and Thai restaurants).

So how does tempeh look, for example, as a protein source? It’s a complete source of protein, about 5 grams in a 28-gram serving. Tempeh is actually a high-fat food when you come right down to it, having a macronutrient ratio of 20 percent carbs-47 percent fat-33 percent protein (now that you’re an expert on MRs!). Four ounces, or about 112 grams, of tempeh contains a lot of Omega 6 fat and has a poor n-6:n-3 ratio of more than 10 to 1. It’s a decent source of vitamins and minerals.

Natto has a similar profile, but is more nutritious in terms of vitamins/minerals and has an almost equal amount of protein compared with tempeh, with the same problem of an unfavorable Omega 6 to 3 ratio (in the form that must be converted, unfortunately at a low rate, to the long chain versions that our bodies really need).

To show you how to analyze food for its protein quality, we’ll do a quick check of lamb, salmon, and bananas with NutritionData. This searchable web database for nutrition information has a good section on its result pages for protein. Figure 7 shows the page for a small slab of cooked lamb, which the site gives a good protein score (anything over 100 is a complete protein).

Lamb gets a good protein score

Figure 7. Lamb gets a good protein score

Many of the amino acids are in lamb in a quantity in excess of a gram, and the four ounce piece of meat has 26 grams of protein, a bit less than a quarter of what a training athlete would need in a day. Salmon is also an excellent source of amino acids, as Figure 8 shows. A six ounce filet has about 40 grams of protein, with more than 3 grams of the important muscle-building amino acid leucine. It also has more than 300 mg of tryptophan, an important biochemical precursor in the synthesis of the neurotransmitter serotonin, as well as the hormone melatonin.


Tryptophan in food may help make you sleepy before bedtime, because serotonin has a calming effect, and melatonin is a hormone that plays a role in sleep regulation.

A salmon filet cleans up with essential amino acids

Figure 8. A salmon filet cleans up with essential amino acids

image with no caption


The absorption during digestion of amino acids is quite slow—anywhere from 3 to around 10 grams per hour (that’s only 12 to 40 calories per hour), depending on how much you weigh and whether the protein has a fast (whey protein) or slower (raw eggs) absorption rate—compared with fats (about 14 grams per hour) and carbs (60 to 100 grams per hour, in terms of a glucose drink). So, if you eat 40 grams of protein, your body may take about eight hours to absorb and utilize the amino acids.

Just for the sake of comparison, let’s check out the amino acid content of a starch: bananas. A banana actually contains all the amino acids, but in very small amounts: less than 100 mg each (a large banana, after all, provides just 1.5 grams of protein). As shown in Figure 9, though, the banana scores more than 30 grams of carbs, including over 6 grams of glucose and fructose, and even a little maltose.

A large banana chalks up the carbs on NutritionData

Figure 9. A large banana chalks up the carbs on NutritionData


A medium-sized sweet potato has 1/10th the glucose and fructose of a large banana. A banana is a good source of potassium, however, so that’s the trade-off.

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