In many articles on the site, I go into a rather great deal of detail on various aspects of human nutrition and the various nutrients that comprise it. However, I find that it’s often exceedingly useful to go back to basics and discuss the fundamentals (this applies to all topics, not just nutrition). Where appropriate, I’ll point readers to other articles on the site (or my books) which discuss a given topic in more detail than I want to cover here.
To keep the piece manageable, I’m going to divide it into two parts with Part 2 being run on Thursday. Today I want to look at the issue of essential vs. non-essential nutrients as well as protein and carbohydrates. On Thursday, I’ll tackle the issue of dietary fats along with everything else (fiber, alcohol, vitamins and minerals).
Essential vs. Non-essential Nutrients
The body has a requirement for somewhere around 60 nutrients on a daily basis for normal functioning. Please note: as nutritional science has progressed, it’s now become apparent that many, many more nutrients may contribute to optimal health, although they are not necessarily required for survival. Put differently, you can live without consuming them but you might be healthier or perform better if you did eat them.
I should also mention that this list of 60 nutrients includes things such as air and water that, while they aren’t considered as nutrients per se, are usually not an issue. Put differently, if you’re having issues obtaining adequate amounts of air or water, you have bigger problems to deal with.
Of more relevance to today’s article, nutritional science often groups nutrients into the categories of essential and nonessential (recently the terms indispensable and dispensable have come into vogue) which is what I’d like to discuss next. For quick summary, there are roughly 8 essential amino acids, 2 essential fatty acids, a host of vitamins and minerals and a few others substances that are required on a daily basis. You might note that carbohydrates were not listed as an essential nutrient, a topic I’ll come back to below.
So what is an essential nutrient as opposed to a non-essential nutrient? I’m actually going to answer that by explaining what a non-essential nutrient is first. Contrary to what it sounds like, the term non-essential (or dispensable) doesn’t mean that the nutrient isn’t essential for life; rather, it’s not essential that the nutrient be obtained from the diet itself.
Translating that into English, there are some nutrients (such as glucose, certain fatty acids and just over half of the amino acids) that can be made in the body from other sources. For example, many amino acids can be made in the body via metabolism from other amino acids; as well, glucose can be made in the body from a number of different substances. So while these nutrients are essential for life and survival, it is not essential that they be obtained from the diet.
At the same time, there are nutrients that cannot be made by the body (the vitamins and minerals are examples, so are the essential fatty acids and roughly the other half of the amino acids) and are hence considered essential nutrients. That is, it is essential that they be obtained from the diet (generally on a daily basis).
In short, to be considered essential, a nutrient must meet two primary criteria:
- That nutrient is required for survival
- That nutrient cannot be made in sufficient quantities (or at all) by the body
So if a nutrient isn’t required to keep you alive, it’s not essential (even if consuming it improves health or what have you). If it’s required for life but the body can make sufficient amounts of it, it’s still not essential to get it from the diet; hence it is not an essential nutrient. Only when a given nutrient is both required for survival and can’t be made in the body in sufficient amounts is it an essential nutrient in terms of what I’m talking about here.
Although I want to keep this piece focused on the basics, I should probably mention one odd exception which is Vitamin D (currently getting a lot of press, and for good reason, in various places). Vitamins and minerals, generally, can’t be made in the body and must come from the diet. But while Vitamin D can be obtained from the diet (many foods are fortified with it), and is an essential nutrient, it is actually made by the body in response to sunlight hitting the skin.
I want to make it clear that the above is a bit of a simplification and the topic of essential and non-essential nutrients can be made considerably more complicated. For example, some nutrients can be considered conditionally essential. That is, under normal conditions, the body may make plenty of a given nutrient (meaning that it is not required that the nutrient come from the diet) but under other conditions the body needs more than it can make. Under those conditions (usually involving things like disease and severe trauma), a nutrient that is normally non-essential becomes essential (must be obtained from the diet). Hence conditionally essential.
The word protein come from a Greek word meaning “the first” which is meant to signify its primary role in human nutrition. While you can survive rather extended periods without carbohydrate or fats in the diet, a long-term lack of protein intake leads to a loss of body tissue (muscle and organ protein), function and eventually death.
Whole dietary proteins are made up of smaller units called amino acids of which ~20 occur in the diet (there are many more that occur in the body). Of those 20 or so amino acids, roughly eight are considered essential meaning that they must come from the diet on a daily basis. Under certain conditions, such as stress and trauma, some amino acids also become conditionally essential; glutamine is perhaps the most commonly cited example with much higher amounts that can be made in the body being required under those kinds of conditions. There are other examples but few would be relevant outside of some very very specific situations (usually involving severe malnutrition or disease).
A primary distinction between protein and carbohydrate/fat is that only protein contains dietary nitrogen (which is technically an essential nutrient). Since humans can’t ‘fix’ nitrogen from the air like plants, we have to obtain it from the diet. And that nitrogen is found in the individual amino acids that make up whole food proteins. Also, while there can be some interconversion of protein (more accurately, amino acids) to carbs or fat (this last one is very rare), neither carbs nor fat can be made into amino acids.
Proteins/amino acids have a number of crucial roles in the human body but most of them are structural (meaning the protein is used to build things). Many hormones are made of protein (some examples are IGF-1 and Growth Hormone), your organs, muscles, skin and hair all contain protein; protein has numerous other roles in the body as well. Protein can also be used to produce energy in the body, usually by conversion to other nutrients (almost always glucose). For example, during long-term aerobic exercise, the breakdown of amino acids (specifically leucine) can provide 5-10% of the total energy generated.
Something to note is that, in contrast to carbohydrate (which is stored in both muscle and liver) and fat (which is stored on your butt and stomach), there is no real storage form of protein unless you count the relatively small amount floating around in the bloodstream and the protein that makes up your muscles and organs. But this isn’t a true storage form like for carbohydrates and fats since, in general, breaking down body protein is a bad thing (as I mentioned above).
In the diet, protein is found to some degree in almost all foods with the exception of pure fats like vegetable oils and such and some totally refined carbohydrates such as candy (e.g. jelly beans). Fruits and vegetables contain fairly small amounts of protein (perhaps a gram or two per serving) while beans and nuts can contain significant amounts of protein. But most people in modern society get their protein from animal based products: meat (red meat, chicken, fish), milk, cheeses, etc.
In terms of caloric content, protein has traditionally been assigned a value of 4 kilocalories/gram (~16.8 kj/g) but this is currently a topic of some debate. Because of how it is digested and assimilated in the body, at least one researcher is suggesting strongly that protein be given a lower caloric value (roughly 3.2 kcal/g or 13 kj/g) than the traditional value.
The term carbohydrate refers to a number of different organic compounds ranging from simple sugars (e.g. glucose and fructose) to disaccharides (e.g. sucrose, lactose) all the way up to starches (long chains of individual carbohydrate molecules bound together). Because of it’s chemical structure, you will often see carbohydrate abbreviated as CHO (for carbon, hydrogen, oxygen).
In the body, carbohydrate’s role is primarily energetic, that is it provides energy (through breakdown) in various tissues of the body. Most tissues in the body can use glucose for fuel and, quite in fact, most will use glucose if it is available (they will switch to using fats or ketones if glucose is not available in sufficient amounts). A few tissues of the body can only use glucose for fuel.
And while the above might suggest that dietary carbohydrates are essential, this isn’t the case. Recall from the discussion above that, to be considered essential a nutrient must not only be required by the body but cannot be made in sufficient quantities. And, as I’ve also discussed elsewhere, the body is able to produce some carbohydrate from the breakdown of other nutrients, specifically about half of the amino acids, glycerol (the backbone of both dietary and body fat) and lactate.
In general this process (called gluconeogenesis which simply means the production of new glucose) is able to cover the body’s basic daily needs. As well, with low-carbohydrate diets, there is a whole body shift in fuel use from carbs to fats and ketones which reduces carbohydrate requirements. This is discussed to some degree in nearly all of my books but the greatest detail can be found in The Ketogenic Diet.
I would finish by noting that high-intensity exercise tends to increase carbohydrate requirements beyond what the body can make putting carbohydrates into the conditionally essential category I discussed above (e.g. the body needs more than it can produce itself). For those individuals who wish to perform high-intensity activity such as intensive weight training or even high intensity metabolic work, some amount of carbohydrates generally becomes required in the diet. The issue of daily carbohdyrate requirements is discussed in much more detail in How Many Carbohydrates Do You Need?
Carbohydrates can be stored within the body in the liver or muscle as glycogen (a long chain of glucose molecules bonded to each other) and is found in small amounts (~5-10 grams total) as free glucose in the bloodstream. Liver glycogen exists primarily to help maintain blood glucose levels while glycogen within skeletal muscle can only be used by the muscle that it’s stored in; it can’t be released back into the bloodstream.
Dietarily, traditionally carbohydrates have been divided somewhat simply into two major categories (this is especially true in athletic subcultures but is often used generally) which are fibrous and starchy. Please note that this is mainly a division of convenience but it tends to be useful practically so I’ll stick with it.
Fibrous carbohydrates generally refers to vegetables which, with a few exceptions, tend to contain very small amounts of digestible carbohydrate while containing a lot of fiber. Pretty much any vegetable you care to name (with the handful of exceptions mentioned next) will fall into this category of carbohydrates and it’s often stated that you can eat these types of carbohyrates ‘without limit’ due to their generally low caloric content. I’ll come back to this shortly.
Starchy carbohydrates are, more or less, everything else: breads, pasta, rice, and grains, basically any carbohydrate that contains a good bit of digestible carbohydrate. I should note that there are a few starchy vegetables such as carrots, peas, corn and potatoes: vegetables which contain larger amount of digestible carbohydrate and which need to be counted as starches in terms of real-world meal planning. Fruits, while not technically a starch, are usually grouped with starches since they contain quite a bit of digestible carbohydrate (the majority of which are simple sugars).
Explaining the caloric value of carbohydrates can be somewhat confusing. Starchy carbohydrates are generally assigned an average value of 4 calories per gram (16 kj/g) although this can vary slightly from food to food. Fiber is where it gets more confusing; as I recently discussed in Fiber – It’s Nature’s Broom, some types of fiber can be broken down to other things in the intestine and, recently, fiber has been given a caloric value of 1.5-2 kcal/g (~6.3-8.4 kj/g). While this isn’t a large amount given most people’s average fiber intake, for people who are eating enormous amounts of vegetables (which don’t just contain fiber, mind you), the calories can start to add up.
And with those topics covered, I’ll stop here for today. On Thursday, I’ll take another quick look at dietary fats along with the ‘everything else’ category of human nutrition: alcohol, vitamins, minerals and fiber (again).