The below is a slightly abridged and edited version of Chapter 15 from my book The Thinking Person’s Guide to Fitness
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Intermediate Nutrition Theory
The principles from Part II of this book — avoiding processed food, focusing on sources of protein and produce, and learning to accept hunger — are great rules of thumb for making healthy meal choices. A more systematic understanding of nutrition is required, however, to make truly optimal decisions. This means delving into some modern nutrition science. In this chapter, we will discuss the most elemental ways of describing and measuring the main nutrients and energy sources in food, as well as how your body utilizes these elements.
First we will examine the calorie, which is a means of measuring how much potential energy is in a particular food. And while the calorie is the simplest way of measuring food — it’s just one number to describe a single aspect of a food — the concept is less simple than many people think, given how your body processes and utilizes food.
After the calorie, we will consider the macronutrients: fat, carbohydrates, and protein (along with everyone’s favorite topic: alcohol). These different macronutrients are, essentially, the different types of molecules that food is composed of, and each supplies different things to your body.
Calories
The single most important food metric is the calorie. The calorie measures how much energy is in a food, and obtaining energy is the primary reason we eat food. Various nutrients and vitamins and minerals are all important for health as well, but really — and most essentially — we eat food in order to power our bodies. That power comes from the energy that is embodied in food.
When first defined in nineteenth century, people wanted to understand the energy content of food in order to ensure that everyone got enough to eat. Of course, in the newly upside-down, ultra-abundant world we now find ourselves, everyone is instead concerned when the amount of energy in a food seems “too high.” Calories are nowadays something that almost all of us are trying to minimize.
The sidebar below has technical information for those interested, but what is important is simply to know that (1) a calorie is a unit that says how much energy you can get from a specific food; and (2) from an energetic point of view, one calorie will always be equivalent to any other, regardless of the type of food that contains it. For example, the amount of energy in one calorie of hamburger meat is the same as that in one calorie of the bun.
The calorie only measures the energy level in a food. So different types of food will have different amounts of calories for a given weight. The food you eat consists of four different types of energy-producing macronutrients, each of which has a specific level of calories per gram of macronutrient. The approximate values for each are worth memorizing:
• Fat: 9 cal/gram
• Protein: 4 cal/gram
• Carbohydrates: 4 cal/gram
• Alcohol: 7 cal/gram
Of course, except for truly dry items, almost all food also contains a substantial amount of water. Water, though critical for survival, does not provide energy. In addition, some foods also contain fiber and other nutrients that your body will not directly absorb and which therefore do not contain calories in the sense that we care about them. The above caloric values are for the weights of the macronutrients alone, but you cannot simply weigh a food and then multiply the number of grams by the calorie levels above.
One hundred grams (about 4 ounces) of broccoli, for example, only has about 8 grams of actual caloric-containing macronutrients. The other 92% of broccoli is almost all water, along with a little fiber and trace amounts of various vitamins and minerals. Even a skinless chicken breast, which is as close to “pure protein” as one can get in a raw food item, is almost 2/3 water: 100 grams of chicken breast has 31g of protein, 3g of fat, and no carbs, leaving 66g of water in the breast.
Except for highly processed things like table sugar and dried foods like chips or jerky, the weight of the food you eat is always substantially higher than the total weight of macronutrients. This is one reason, by the way, for why it is virtually impossible to overeat vegetables: they contain massive amounts of water, bound up in nutritious fiber. They are therefore always very low in calories, ounce for ounce, versus all other foods.
A good exercise for getting familiar with calories is to take a few food labels and add up the calories in each of the macronutrients, and then see how they compare to the calories listed. Multiply the number of grams of fat in a serving by 9, and the protein and carbohydrates by 4, and see if you get the total number of calories the label states.
If you do this exercise with a few different items you will find that the sum you get from your macronutrient math is almost always very close to the number of calories the label states. There are rounding errors, of course, especially when serving sizes or total calorie counts are small, but the numbers should always be within about ten percent of each other.
Given how we tend to think of calories as a “scientific” notion, though, ten percent is not really all that precise. The issue is that, in addition to rounding errors, the reality is that not all forms of each macronutrient have precisely the same number of calories. The whole numbers I provided are the “standard issue” calorie counts provided by nutritionists, but they simplify things a bit. Plus, while some forms of fiber are non-digestible and have no calories, other forms are and do. No matter how precisely you might try to measure your caloric intake for a day, you’ll always be slightly off.
The imprecision in how many calories you burn in a day is even more pronounced. Between your resting metabolic rate, various subconscious activity levels, the amount of energy required to process different types of food, and the change in your purposeful exercise from one day to the next, it is simply not feasible to know exactly how many calories you expend in a day.
Any apps that calculate the calories you eat should be taken as approximations; they can be worthwhile tools, just do not get wrapped up in the precision that they implicitly claim. More importantly, you should completely ignore any calculators that claim to tell you how many calories you expend. Having an app that purports to track the calories you burn is at best a diversion from what you should be focusing on, and at worst a machine for giving you incorrect information that might thwart your goals.
All those caveats aside, though, you should learn how to count calories, even if only to develop a better intuition about what you are eating. The next chapter covers how to best do this. But the point of counting calories isn’t that you can find out exactly how many calories you ate in a given day — that is virtually impossible.
Instead, counting calories is important because, despite the imprecisions, it is the best means for planning and tracking your food intake, and for controlling your portion sizes. There’s no better method out there. Just remember that dealing with calories is not an end in itself, and don’t get carried away with it. The calorie is a tool, and it is not a particularly precise one.
Macronutrients
The calories you consume all come from various macronutrients. And as the prefix “macro” implies, macronutrients are simply those chemical elements required by your body in large quantities. This distinguishes them from the micronutrients, such as vitamins and minerals, which we only need in incredibly small quantities — often less than 1 milligram a day, versus 100 grams.
These macronutrients are the sources of energy we use each day. The standard classification of macronutrients includes three types: protein, fat, and carbohydrates (often shortened to “carbs”), each of which is discussed below.
However, I am also adding two others to the standard mix. One is fiber, which is a type of carbohydrate important for your health and thus worth paying special attention to. The other is alcohol, which is definitely not important for your health but which does contain energy (and thus calories). Knowing about these helps round out a full understanding of macronutrients.
Protein
Protein is the essential building block of your body: every single cell is made up of various forms of protein. In addition to constructing your body, proteins are also used in all kinds of life-supporting processes: transporting molecules between cells, energizing your metabolism, sending information from one part of your body to another, and so on.
From a chemical point of view, all proteins are made up of chains of amino acids. There are a total of twenty-one different types of amino acids in all — yep, all forms of life (as we know it) are made up of only twenty-ish different proteins. Amino acids, in turn, are complex chemical compounds containing chained molecules of just nitrogen, hydrogen, and oxygen. Despite such simplicity in elements, each specific amino acid has a slightly different structure, giving them each unique properties.
Because your body is constantly breaking down and repairing itself, and because proteins are used in so many processes, you need a constant supply of them. The average protein molecule in your body only lasts for a couple of days; even those that make up your cells and organs do not stick around for long. You can observe this process in your hair and fingernail growth, but it is happening everywhere: even the cells in your seemingly permanent bones are constantly being renewed.
You get the protein for all this cellular renewal and other processes from the food you eat, which is why protein is an essential part of any nutritional plan. Moreover, unlike fat and carbohydrates, your body does not have any means of storing protein for later use, and so it is best consumed every day.
Our body is capable of rearranging the molecules of some types of protein to create the majority of the amino acids that we need, but there are nine which we cannot make ourselves and thus must obtain through food. These nine amino acids are called “essential” amino acids, and the other types are considered “non-essential.”
You may have heard at some point about “complete proteins” — these are protein sources that contain all the essential amino acids in a reasonable ratio. But unless you are a vegan, you really do not need to worry about the types or ratios of amino acids in your food — if you are eating some animal products and getting the recommended amount of protein in your diet, then you are getting all the necessary amino acids.
The best protein sources are meats; eggs and dairy (milk, cheese, yogurt, etc) are also excellent. These animal products should be your primary sources of protein. Secondary sources include beans and nuts/seeds — for vegans, these are your main source, so you need to be much more careful about eating plenty of them. Beans in particular are a broad category: tofu and other protein-rich soy products are technically from a bean, for example. Plus, protein powders made from soy, rice and peas are all good vegan sources of protein as well, as an ingredient in smoothies or other recipes. (Non-vegans can include whey and egg protein powders, if they are looking for ways to increase their protein intake in smoothie form.)
The amount of protein you should eat each day is less controversial than fat or carbs. The US government’s minimum RDA (recommended daily allowance) is about 70 grams a day, but this is truly a minimum and anyone who is even moderately active should aim for more. At the other extreme, bodybuilders typically use the rule of thumb that you should eat 1 gram per pound of your weight, and there is little reason anyone should need more than that.
The best evidence out there suggests that even someone doing serious strength training does not need more than about 3/4 of a gram per pound of bodyweight, and this is what I personally aim for. But the math is easier with the bodybuilders’ formula, and there is no harm in eating that much as well. So if you are 160 pounds, for example, you should aim to eat about 120-160 grams of protein a day.
Also, virtually all foods have a little protein in them, so you could aim for your “primary protein” sources to be about 3/4 of your total desired protein: this would mean about 90-120 grams for a 160 pound person, which is roughly 12-16 ounces of meat a day. (For reference: a 6-ounce chicken breast has about 40 grams of protein, a 5-ounce can of tuna has about 30 grams, and a glass of milk or ounce of cheese has around 8 grams.)
Regardless of the exact number, if you are trying to determine the ratio of macronutrients your overall diet should consist of — an exercise we play with in the next chapter — protein should always be the first quantity you choose, and then you can build your other macronutrients around that.
Fat
Fat is another truly essential macronutrient: like protein, you need it to survive. It’s necessary for the absorption and transportation of many vitamins and minerals, to make certain hormones that regulate your body, and it’s also used along with protein in the structural maintenance of tissues and cells. Fat can also be used by the body as an energy source, especially for low-intensity activity, as we’ll see in Chapter 18.
Fat can be classified into one of two types: saturated and unsaturated. Unsaturated fat is in turn typically divided into several types: monounsaturated, polyunsaturated, and trans-unsaturated. These divisions are often used as a way of distinguishing the different types of fats that we consume, though the actual chemical makeup of fats is more complex than these simple divisions might imply.
Just as all proteins are made up of amino acids, all fats are made up of fatty acids. Fatty acids, in turn, are chains of carbon, hydrogen, and oxygen atoms. The different types of bonds that make up the molecular chains and combine them into fatty acids are what create each fat’s characteristics and thus defines the type of fat that it is.
The primary distinguishing factor in the classification of fats is the temperature at which they become liquid. Saturated fats have higher melting points than unsaturated fats, and tend to be solid at room temperature. For example, most fats found in meat, butter, and cheese are examples of saturated fat. On the other hand, oils that are liquid at room temperature, like olive oil or sesame oil, are examples of unsaturated fats. Keep in mind, however, that most foods you eat are mixtures of various types of nutrients. So while cream is liquid, it is in fact a saturated fat that happens to be “mixed” with water. Likewise, though nuts themselves are solid, the oils in them tend to be unsaturated.
The health distinction between naturally occurring saturated and unsaturated fats is fairly minimal, actually. Despite the scare-mongering in the late twentieth century about saturated fats, long-term research has shown that for most people eating an overall healthy diet there is no real concern with consuming them.
On the other hand, trans-unsaturated fats (popularly known as “trans-fats”) are indeed something which should be avoided. While trans-fats occur in minute quantities in nature, laboratory-made versions became quite common ingredients of many processed foods in the last half of the twentieth century, helping to cheaply extend shelf-life. Trans-fats have recently been shown to be detrimental to your heart health, and should be avoided. If you are already keeping processed food consumption to a minimum, however, then you don’t need to worry about them.
In addition to the functions mentioned above, fats also provide a source of energy for our daily activities. In fact, our bodies have evolved to very effectively use fats for the majority of our energy needs, as well as to store it for later use. And unlike protein (which cannot be stored) or carbohydrates (which can only be stored in limited amounts) we are capable — as most of us are well aware — of storing massive amounts of fat.
Because fat is so energy dense (recall that fat contains 9 calories of energy per gram, versus 4 for carbohydrates), it is a naturally great form of energy storage. Moreover, our bodies are capable of converting carbohydrates (and, to some extent, protein) into fat as well, allowing even more storage of the energy we consume.
Our body fat is kind of like an expandable “gas tank,” which was great for our ancestors who needed to feast when times were good in order to last through the forced fasts of famine. In our current world of over-abundance, this capability to store large amounts of fat is generally considered a net negative, but it once did — and in fact still can — serve an important purpose.
Even though the fatty acids of fat are essential to life, since the body can access its stored fat, the regular consumption of fat in food is not as critical as it is for protein. That said, fat does tend to be both satiating and delicious, and it does help with the absorption of many micronutrients, so it is generally a good idea to get at least a little fat with every meal, and not to engage in extremely low-fat dieting. A good rule of thumb would be to ensure that at least 20% of your calories each day come from fat.
Most all protein sources include some fat in them, and protein sources like nuts, dairy, and beef often have quite a lot. So you do not necessarily need to add a lot of fat to your diet in order to meet your nutritional needs. But adding a sensible amount of fat — a tablespoon or so — to salads or lean meats makes sense both for nutrition and flavor. Use whatever type of fat you prefer.
Carbohydrates
Unlike protein and fat, both of which contain nutrients essential for survival, carbohydrates do not contain anything truly required for you to live. On their own, carbohydrates only provide energy, which you could also get from fat or protein, and so eating carbs is not really “essential.”
That said, carbohydrates are very useful for powering most forms of strenuous exercise, as I will describe in Chapter 18. Moreover, high-quality carbs almost always contain lots of vitamins and minerals, as well as a good dose of fiber. Thus, while carbohydrates per se may not be essential for survival, including the right types in your diet will promote good health as well as athletic performance.
The “right type” of carbohydrates basically boils down to the standard distinction between and simple and complex carbohydrates. This classification isn’t a true dichotomy, with all forms of carbs clearly being either one or the other type. Instead, the split between complex and simple carbs is more of a spectrum, with most carbohydrate-rich foods falling somewhere between the poles of extremely simple (such as sugar or white bread) and extremely complex (such as a highly fibrous vegetable like cabbage).
All carbohydrates are made up of carbon, hydrogen and oxygen atoms. These three molecules form various types of sugars, such as glucose and fructose, which can be combined into larger compounds such as starches.
The distinction between a simple and complex carbohydrate, though, is not whether the carbs are in the form of sugar or starch — pasta, bread, and rice are as about as simple a carb as table sugar — but the extent to which these sugars and starches are bound up with another type of carbohydrate called cellulose. Cellulose is the main structural component of cell walls in plants, and is basically what nutritionists call “fiber.”
Fiber
Fiber is officially considered a type of carbohydrate, but it is special enough to be thought of as a macronutrient in its own right. Fiber is the nutritionists’ term for cellulose, the structural element of cell walls in plants. It’s not processed by your body, but is nonetheless highly valuable to your overall health and fitness, both directly and indirectly.
One indirect benefit of fiber is that foods with a high fiber content tend to also be foods with lots of vitamins and minerals. But there’s also a more direct and immediate benefit: fiber binds together with the simpler sugars and starches, so foods that include a lot of fiber cause your body to more slowly digest those simpler carbohydrates. This prevents the sugar rushes (and later crashes) that you get from foods like candy and pasta, which can whipsaw your energy levels and cause hormonal changes that promote fat storage (a topic discussed in Chapter 21).
The main reason that fiber is important, however, is that it promotes your gut health (also discussed in Chapter 21). The microbiome — a world of billions of bacteria — inside your gut is crucial for the functioning of every part of your body, and it is important to keep it well nourished. While your body does not process fiber, your microbiome uses it to keep itself healthy, which in turn keeps you healthy.
There are two types of fiber: soluble and insoluble. Insoluble fiber does not dissolve in water, and soluble does. While both promote your gut health by helping to maintain an environment conducive to the ecosystem of microflora living there, soluble fiber is especially important since it provides food for those bacteria. And while insoluble fiber ends up passing through you without absorption (which is why fiber content is traditionally subtracted from the calorie counts associated with carbohydrates), soluble fiber is indirectly absorbed — your own cells might not use it, but your bacteria does: it lives off the stuff.
While “probiotics” — actual bacteria that can be introduced to your gut via fermented foods like yogurt and sauerkraut — get most of the trendy press for its benefits to gut health, soluble fiber — known as “prebiotics,” since it feeds the existing bacteria — is at least as important. In addition to being present in most any produce, foods such as oatmeal, beans, and chia seeds are also all good sources for these prebiotic soluble fibers, and worth including in your diet on occasion.
Carbohydrate Consumption
When your body breaks down the carbohydrates you eat, they are all eventually turned into a form of simple sugar. With complex carbohydrates, the sugars and starches are bound up with lots of fiber; in contrast, simple carbohydrates have zero, or very little, fiber. Except for when you are engaged in long-lasting and intense exercise (which is the only time simple carbohydrates are preferable), complex carbohydrates are always preferable, nutritionally speaking, to simple ones.
Carbohydrates, like fat, can be stored for later use. However, while fat storage is practically unlimited, carbohydrate storage is limited to your muscles and your liver, which can only hold so much. Your body breaks down all carbs into glucose (ie, sugar) and uses it for energy; excess glucose can be converted to glycogen and stored in the liver and muscles.
Depending on your size, your liver can store about 4-6 oz (100-150g) of glycogen, and all of your muscles in total can store about four times what your liver does. If these stores are full, then excess glucose will be converted to fat and stored.
Good sources of carbohydrates include grains, tubers, and produce. Produce, in the form of fruits and non-starchy vegetables, was thoroughly discussed in Part II. And while the amount of carbs that is contained in most produce is fairly low compared to the fiber and water content, until and unless you are engaging in hard exercise for an hour or more, you can easily get enough carbohydrates — along with fiber — from just fruits and vegetables. For anyone not doing any intense activities, there’s really no need to consume more than about 30-50 grams of carbohydrates per day.
When your activity levels are high, though, grains and starchy tubers (potatoes and yams, for example) are the ideal way to healthily increase your carbohydrate intake. The less refined your grains are the better — whole grains contain more vitamins and minerals and fiber than their “white” versions. Outside of athletes in serious training or competition, there is not really any nutritional reason for consuming highly processed grains or sugar, which provide nothing but energy.
Alcohol
While alcohol is not normally considered a macronutrient, it is worth discussing since it contains energy, and thus calories. It does not, however, contain nutrients. Like refined sugar, alcohol is a form of “empty calories” — something which has no nutritional value beyond its caloric energy.
In fact, alcohol is technically just a type of sugar, made up of the same carbon, hydrogen and oxygen molecules. But unlike sugar (and all other foods), alcohol is treated by your body like a kind of poison. If it is in your bloodstream, your body will process it first in order to remove it from your system, using the liver to do so and providing energy in its processing. So long as there is alcohol is in your system, any other food your body is processing will be stored as body fat instead of used for energy.
It would be incredibly hypocritical of me to write that you should never drink alcohol, so I am not going to do so. But it is important to be aware of the various ways in which it negatively impacts your health and fitness, and to treat it like the vice it is — with care and conscientiousness.
Two negative effects of alcohol were alluded to above. Firstly, it is stressful on the liver. While the liver is capable of handling a certain amount of alcohol processing without becoming damaged, regular binge drinking (or even daily “moderate” drinking) does tax the liver and can thus cause long-term problems. Secondly, while the process of burning off the alcohol in your system is happening, your body is storing any other calories in your system as fat. Combining alcohol with a large meal is a recipe for fat gain. This isn’t technically terrible, since you can always access that body fat for energy later. But for those who would rather not be burning off excess body fat if they don’t have to, consuming alcohol around the time you eat is counterproductive.
Another problem with consuming alcohol if you are trying to lose fat is that your willpower starts to dissipate, along with all your inhibitions. A second drink can easily turn into a third, and that third into more. Likewise, after a few drinks, you’ll more readily find excuses to overeat.
Finally, having more than a glass or so of alcohol a night tends to interfere with both sleep and morning exercise programs and thus inhibits the formation of the good habits you need to build and maintain. It’s not impossible to drink heavily on a regular basis and still be fit, but it definitely makes things harder.
Alcohol has 7 calories per gram — but this is per gram of pure alcohol, and alcohol always is at least partly water. Even high-proof whiskey is about half water. Generally speaking, a “serving” of alcohol, whether in the form of hard liquor, wine, or beer, usually contains about 100 calories of alcohol. And for most people, it takes about an hour to burn off this energy. (This is why you can drink roughly one drink an hour without getting drunk: by the time the second drink rolls around, the first is out of your system.)
However, unless you like hard liquor neat or on the rocks, your alcoholic drinks will contain both alcohol and carbohydrates. Wine contains just a few grams per glass, whereas a 12-ounce beer might have half as many calories from carbs as it does from the alcohol. And cocktails, especially sweet or fruity ones, often have more calories from sugar than from the alcohol. So, for those looking to minimize fat gain and caloric intake while drinking, the least-bad drinks will be wine or — better — hard liquor mixed with water or club soda.