A Primer on Dietary Carbohydrates – Part 1

Having previously done a fairly detailed Primer on Dietary Fats, I wanted to do something similar on the topic of carbohydrates (in the future I’ll do one for protein as well).  In this article, I’m not going to look at many of the debates surrounding the issues of carbohydrate intake (in terms of body weight, body fat, or health), you can read Carbohydrate and Fat Conteroversies Part 1 and Carbohdyrate and Fat Controversies Part 2 for somewhat of an examination of that.  Rather, I just want to focus on some basic definitions and concepts since there tends to be a lot of general confusion over the topic of carbohydrates.

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What is a Carbohydrate?

The term carbohydrate is sort of an overall classification referring to a number of different organic compounds, which I’m going to detail below.   You may often see the abbreviation CHO (for Carbon, Hydrogen and Oxygen) to refer to carbohydrate.  Although fiber is a carbohydrate, I’m not going to discuss fiber in detail in this article; rather I’d refer you to Fiber – It’s Natures Broom for a detailed look.

As I have discussed in many articles on the site, the primary role of carbohydrate in the body is energetic, that is it is broken down in cells to provide energy through a variety of pathways.   At the same time, strictly speaking, carbohydrate is not an essential dietary component; that is, you can survive without eating it at all (an explanation of essential vs. inessential nutrients can be found in A Primer on Nutrition Part 1).  How many carbohydrates should be consumed in the human diet is a topic of endless debate and controversy, I’d refer readers to How Many Carbohydrates Do You Need? for a detailed look at the topic.

Now, another term that is sometimes used to describe carbohydrates is saccharides and, with that trivial note made, there are three primary classes of carbohydrates which I’m going to first list and then describe in more detail below in terms of what they are, what they do in the body and where they are found in the food supply.

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Fiber – It’s Natures Broom

Years ago I remember lamenting (and writing somewhere) that I was fairly sick of reading research papers on how eating more fiber was good for people, how it was time for nutritional science to move into relatively more interesting things than a topic that had literally been beaten to death.

Thankfully, soon thereafter leptin was discovered and nutritional researchers could start looking at things more interesting than why eating high-fiber vegetables were good for you (a nutritional tidbit that I file under the ‘Grandma was right’ category).

Even so, there is still some confusion regarding fiber out in the world of nutrition regarding fiber.  And boring or not, it’s a topic worth clearing up.  So today I want to take a fairly comprehensive look at dietary fiber, what it is, what it does in the body, how it impacts on things like body composition (and health to a lesser degree) and finish by looking at some (admittedly vague recommendations).

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What is Fiber?

Generally speaking, fiber is included within the category of dietary carbohydrates (many athletes or bodybuilders divide carbohydrates into starchy and fibrous for example).  But fiber is distinct enough to be considered separately from other types of digestible carbohydrates.  Perhaps surprisingly, defining what is and isn’t a fiber is actually a more complicated issue than most would think.

Chemistry, botanical and physiology types all sort of want to use different definitions and spend altogether too much time arguing about what is and what isn’t a fiber.  Since I’m less interested in chemical or botanical issue than physiological ones, I won’t bore people with the details of those of those definitions and arguments.  Rather, I’m interested in the physiological effects and, hence, the physiological definitions.

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How Many Carbohydrates Do You Need?

A perennial question, argument and debate in the field of nutrition has to do with how many carbohydrates people should be eating. While the nutritional mainstream is still more or less advocating a large amount of daily carbohydrate (with fat being blamed for the health problems of the modern world), groups often considered at the ‘fringe’ of nutrition are adamant that carbohydrates are the source of all evil when it comes to health, obesity, etc. They advocate lowering carbohydrates and replacing them with dietary protein, fat or both.

This is a topic that I discussed in some detail in Carbohydrates and Fat Controversies Part 1 and Carbohydrate and Fat Controversies Part 2 and I’d recommend readers take a look at those for a slightly different look at the issue than what is discussed here.

Arguments over recommended carbohydrate intake have a long history and it doesn’t appear to be close to ending any time soon. Typical mainstream recommendations have carbohydrates contributing 50% or more of total calories while many low-carbohydrate advocates suggest far fewer (ranging from the 40% of the Zone diet to close to zero for ketogenic diets).

This article looks at the topic in detail. And while I originally wrote it quite a while back (some of you have probably seen it before), it was nice going over it with fine toothed comb for an update. While the majority of it stands up well over time, I was able to make some slight changes to the values, along with removing some original stuff that wasn’t really relevant. Enjoy.

Introduction

It’s safe to say that most carbohydrate recommendations that you will see are put in terms of percentages, you should be eating 45% of your calories as carbs, or 65% or whatever number is being used.

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Carbohydrate and Fat Controversies: Part 2

In Carbohydrate and Fat Controversies: Part 1, I begun an examination of the argument over carbohydrate and fat intakes in the human diet, explaining that, contrary to popular argument, most extremist stances in this debate are incorrect. In Part 2, I want to continue addressing the issue by looking at both sides of the debate.

Examining Both Sides of the Debate

As noted, the usual argument goes that high-fat diets cause high-cholesterol, heart disease, cancer, obesity and the rest, as evidenced by the high incidence of those disease in modern diets (which are typically high in fat). But that’s a questionable conclusion to draw.

Modern diets are also high in carbohydrates (and mainly the highly refined, high GI, low-fiber stuff that the body often doesn’t handle well), low in fruits and vegetables, and generally contain the wrong types of fats (an excess of saturated and trans fats with insufficient amounts of healthy fats). Such an intake is typically coupled with inactivity, the folks eating them tend to be overweight/obese, smoking and alcohol play a role, etc. That is, there are a number of inter-related factors at work here.

Pinning the blame entirely on fat intake or expecting only a reduction in fat to fix the problem is disingenuous: there are a lot of variables at work here. Some research suggests that the entirety of the problem rests with excessive saturated fat intake with the other variables (activity, fruits and vegetables, etc.) playing a relatively minor role. It’s awfully hard to tease out all of the relationships when there are this many variables at play.

Similar comments can be made in terms of obesity. Fat is more calorically dense than carbohydrates and studies comparing high-fat (40%) to low-fat (25%) meals find that people tend to eat more in the higher fat conditions; this is usually referred to as passive over-consumption and leads to excess calorie intake. These studies have problems, mind you, but that’s beyond the scope of this article. The point does stand, though, that dietary fat is tasty (giving food mouth feel) and folks do tend to eat more of foods that taste good.

But while it’s common to blame obesity on high-fat diets, not all researchers agree. Some cultures have fairly high fat intakes but have no problems with obesity and researchers are starting to realize that fat isn’t the ONLY problem. Increasing intakes of refined carbohydrates (contributing large numbers of calories to the diet), decreasing activity, increasing portion sizes and other factors all contribute. You can’t dismiss an excessive fat intake as part of the obesity problem; it’s simply not the sole factor. I don’t want to get into a massive discussion of the carb versus fat debate in terms of caloric intake, preferring to focus on the health issues here.

The fact is that not all studies link a high fat intake to an increased risk of disease. For example, recent analyses of our ancestral diet (what we ate during 99.9% of our evolution) suggests a much higher fat intake and much lower daily carbohydrate intake. Exact numbers vary depending on what assumptions you use but carb intakes of 20-40% (most of which came from low GI, high fiber fruits and vegetables; grains were almost non-existent), fat intakes of 28-60% (which had a significantly different quality than our current diet), and protein intakes of 19-35% of total calories are the current best estimates.

Studies of extant hunter-gatherer societies show little incidence of any of the diseases of modern society and it’s thought that our evolutionary diet was NOT atherogenic (promoting heart disease) despite the high fat intake.

The reasons for this are many-fold, of course and that’s the key to keep in mind when you consider fat intakes and potential health problems. In our ancestral diet, fiber intakes were monstrous, averaging 100-150 grams per day. As well, despite the high fat intake, the source of that fat was far, far different than our modern intake. Much higher intakes of polyunsaturated and mono-unsaturated fats and far lower intakes of saturated fat were fairly typical. Activity levels were also much higher and folks generally stayed pretty lean. Alcohol intake was low or non-existent, as was smoking. Although our ancestors dealt with various stresses, they didn’t deal with the kinds of chronic stress that occurs in modern societies.

Related to this, studies of the Mediterranean diet have found few problems in terms of heart disease and all the rest despite a relatively high fat intake (40% of total calories). Although the reasons are, as always, multi-factorial some of the contributing factors are that the fat intake is primarily from mono-unsaturated sources (e.g. olive oil).

As well, a tremendous amount of fresh vegetables are typically consumed (with far less reliance on refined carbohydrates). Other factors such as activity, bodyweight, moderate alcohol intake and lowered stress levels probably play a role. Studies of the Alaskan Inuit show similar results, despite an extremely high-fat intake, heart disease is almost unheard of. This has typically been attributed to the high intake of fish oils but there may be genetic adaptations as well.

Of course, some studies on low-carbohydrates diets (which are typically high in fat) will show a big improvement in blood lipid levels; this is especially true for individuals with insulin resistance. I’d note that this effect primarily occurs when weight is lost; in studies of very low-carbohydrate diets where weight is gained, blood lipid levels often get much much worse.

Thus, whether or not you’re gaining or losing weight probably impacts on whether or not dietary fat is a health risk. I’d note that studies in cyclists find that high intakes of saturated fat don’t pose a health problem as long as the athletes are in calorie balance. As I mentioned above, activity (which will affect whether ingested dietary fat is stored or burned off) plays a big role here.

Studies in diabetics are finding that higher mono-unsaturated fat intakes (and lowered carbohydrate) intakes may be healthier than the converse. This, of course, only holds if calories are strictly monitored and controlled to avoid weight gain. When weight is gained, from nearly any dietary approach, blood sugar control in diabetics worsens.

Of course, there’s a flip side to the anti-fat dogma and reducing fat to extreme levels can cause its own set of problems. First and foremost, most people find extremely low-fat diets to be tasteless and this tends to limit adherence in the long-term (as I mentioned above, high-fat diets tend to be very tasty and people frequently eat too much).

And while caloric intake typically goes down in the short-term, folks frequently end up increasing caloric intake because they are hungry all the time. Dietary fat slows gastric emptying (keeping food in the gut longer) although some work suggests that this effect is lost with chronically high-fat diets. Extremely low-fat diets tend to leave people hungrier for this reason.

There is also evidence that the fat-soluble vitamin absorption may be impaired when fat intake is taken too low. And while total cholesterol typically decreases when fat intake is lowered, the decrease occurs in both the good (HDL) and bad (LDL) sub-fractions so overall health risk may not be improved. From a body recomposition or performance standpoint, some studies show a lowering of testosterone with very low fat diets.

There is another set of issues that crops up as well. Again, it relates to the simple fact that people have to eat something. In reducing fat intake, most people increase carbohydrate intake. Most researchers would say that this is just fine as long as the increase comes in the form of unrefined, high fiber, complex carbohydrates. I would say that most researchers need to get out of the lab and look at the real world for a while.

The simple fact is that the majority of people who reduce fat do NOT increase carbohydrate intake from unrefined, high-fiber, complex sources. This is especially apparent in the US (I can’t speak for other countries) where companies rapidly jumped on the ‘fat is bad’ bandwagon and brought tons of ‘low-fat’ high-carbohydrate sources that were highly refined to market.

Such foods may have as many, if not more, calories than the same higher-fat items. Even when they don’t, humans play a cute psychological game, tending to eat more of a given food when they are told it’s low or no-fat.

Recent studies are finding that, when carbs are increased from those sources, other problems show up. In addition to the changes in blood cholesterol I mentioned above (both the good and bad subfraction decrease), the increase in refined carbohydrate intake causes an increase in blood triglyceride levels and small LDL particles; both of which are independent risk factors for heart disease and all the rest. The chronically high insulin levels which commonly occur with such a diet cause other problems including insulin resistance and all of the issues that accompany it.

I should probably note, and this could certainly be an entirely separate article, that the new scapegoat for obesity and all of the health problems in the world is excessive carbohydrate intake, with a lot of the focus on insulin release. I don’t have space here to address that side of the argument, a future topic for another day.

Sufficed to say that while there is certainly an element of truth to this (in that excessive intakes of any nutrient, and that includes refined carbohydrates, is bad), it’s still true that simplistically arguing that ‘fat is good and carbs are bad’ is just as moronic as arguing that ‘carbs are good and fat is bad’. Again, it depends on the context.

Summing Up

Now, I want to make it very clear that I’m not trying to make this either a pro-fat or anti-carbohydrate article or trying to make a low-carbohydrate diet the default choice for anybody. My point is simply that the idea that ‘fat is bad’ and ‘carbs are good’ (or the opposite) is too simplistic to be meaningful.

Not all fat is bad and not all carbs are good. The source, the composition of the rest of the diet, the total amounts you’re eating of each, your activity level and other variables all factor in. Whether you’re talking about health risk or obesity, you can’t simply pin the blame on one factor or the other.

So, under conditions of high caloric intake, with a high intake of refined carbohydrates (meaning chronically high insulin levels), poor quality fat choices (too much saturated fat and/or too little unsaturated fats), little activity, minimal fruit and vegetable intake, etc. a high-fat intake is probably very detrimental from a health standpoint. Sadly, this describes a fairly typical diet in the modern world (especially the US).

In contrast, with reduced or even controlled caloric intake (such that bodyweight goes down or is maintained) and most of the fat coming from unsaturated sources (note: excessive polyunsaturated fats has its own set of problems), a high fruit and vegetable intake, reasonable activity levels, keeping body fat levels down, etc. higher fat intakes may be no problem at all. In some situations, an increased fat intake (again, from healthy sources within the context of activity and a high fruit and vegetable intake) may be beneficial compared to the alternatives (e.g. increasing carbohydrate intake).

Carbohydrate and Fat Controversies: Part 1

Although there are still many Protein Controversies (usually regarding kidney health, bone health, etc.), nowhere in the dietary world is there quite as much controversy as over carbohydrate versus fat intakes.

In this article, I want to look at carbohydrate and fat intake in terms of the various arguments and debates that tend to surround them.

The main controversy here revolves around what amounts of carbohydrates and/or fat are ideal, healthy, recommended, etc. and that’s what I’ll focus on. I’m not going to deal with body composition explicitly in this article, I’ll save that for another day.

Two (or Three) Dietary Camps

Generally, folks fall into one of two camps regarding whether they think carbohydrates or fats are good or bad. For a couple of decades now, the mainstream of dietary advice has been more or less stuck in the mindset of ‘fat is evil and ‘carbohydrate is good’.

Various attempts to promote so-called ‘high-fat’ or ‘low-carb’ diets have usually been shot down as fads although there is increasing research evidence that, at least for some individuals (usually those with insulin resistance) higher fat intakes and lowered carbohydrates may be both beneficial and preferred.

However, for the most part, I’d say that mainstream dietitians are still on the carbs = good, fat = bad bandwagon with higher fat/lower carbohydrate diets being relegated to the diet ‘fringe’.

Both groups can bring impressive (or at least impressive looking) data to the table but, as usual, extreme stances are invariably incorrect and the truth lies somewhere in the middle; this particularly debate is no different.

The third group (and the one I put myself in) recognizes that whether or not carbohydrates or fats are ‘good’ or ‘bad’ depends on the context. The source of the carb or fat, the rest of the diet, the goal of the individual, genetics, activity, etc. all factor into this issue. So while it may be convenient to give simplistic recommendations of the ‘X is bad, Y is good’ variety, simple in this case tends to be incorrect.

Perhaps the most succinct way of describing what I’m going to detail is that there are no good or bad foods only good or bad diets. That is, within the context of one type of diet or individual situation, a specific food may be excellent; under other conditions it may be a poor choice.

What does the Body Require?

So that some of my comments will make sense, I need to cover a smidgen of nutrient physiology, mainly having to do with the issue of carbohydrate ‘requirements’ (a topic I cover in detail in How Many Carbohydrates Do You Need).

As I think I’ve managed to work into every book I’ve ever written, there is no strict physiological requirement for carbohydrates (this factoid is often used by the low-carb diet groups as part of the rationale for their dietary approach).

Most tissues in the body can readily use fatty acids for fuel just as easily as glucose. There are a few tissues such as the renal medulla, red blood cells and one or two other that can only use glucose. However, those cells essentially make their own glucose by recycling lactate (produced from glucose metabolism) back into glucose.

The brain is in its own weird category. Under most conditions, it relies exclusively on glucose. And while it can’t use fatty acids directly, it can use a fatty acid derived fuel in the form of ketone bodies. After roughly three weeks of adaptation to using ketones, the brain may only need 25 grams/day of glucose or so, which can be made by the body (in the liver and kidney) from sources such as lactate, pyruvate, amino acids and glycerol.

Even the American Dietetic Association bible, the RDA Handbook, states that there is no requirement for dietary carbohydrates. Any decent nutrition or physiology book will state the same. Despite this basic biological fact, many researchers and diet authorities still insist that the majority (50-60% or more) of the human diet should come from carbohydrates.

I’ve seen papers where researchers point out that the body requires no carbohydrates which then go on to say that a proper diet should contain at least 50% carbohydrates. It doesn’t make much sense.

At the same time, outside of a small essential fatty acid requirement (a few grams per day from the fish oils, EPA/DHA), fats aren’t truly required by the body either. All of the tissues I mentioned above will use glucose if you provide it (the heart is an exception, almost exclusively relying on fatty acids for fuel) and the body can make fatty acids out of other sources if need be (this pathway isn’t utilized massively in humans, although a few conditions will make it relevant).

So, outside of the small essential fatty acid requirement, one could make an argument for there being no physiological requirement for fats either.

What does the body then require on a day to day basis if there is no real requirement for either carbohydrates or fats? Well, outside of the basics like water and air, roughly eight amino acids are essential to get from the diet, there’s the small essential fatty acids requirements and of course vitamins and minerals. Everything else, strictly speaking is optional.

I would note that, to avoid starving to death, sufficient calories will be required. Since it’s generally unrealistic to consume your entire daily caloric requirement from protein, that means that carbs, fats, or a combination of the two, will generally be needed to supply sufficient energy to the body.

But, as noted above, most tissues in the body show a great deal of flexibility, using carbs when they are available and fats when carbs aren’t available. Note also that the body has its own store of fuel, primarily in the form of body fat that is mobilized when sufficient amounts of other nutrients aren’t available.

So Why Do Most Argue that Carbs are Good and Fats are Bad?

Despite the fact that there is no physiological requirement for carbohydrates in the human diet, the most common dietary recommendation in modern times is generally to reduce fat intake and increase carbohydrate intake. I’m going to address the issue starting from that standpoint.

A good question might be why is this stance taken. While I can’t read the minds of these folks (and I hate to contribute to grain lobby USDA conspiracy theories), I think the reasons is actually fairly simple: we have to eat something.

There’s usually a limit to how much protein can be reasonably consumed (and most authorities seem to be against ‘high’ protein intakes as well) so that means that the rest of the diet (in terms of energy) must come from either carbohydrate or fat.

In the 70’s, the stigma against dietary fat started to develop and it all pretty much went from there. Fat was implicated as the cause of heart disease, stroke, obesity, you name it and excessive fat intake was blamed.

Since people have to eat something and because of the general stigma against a high fat intake (some of which is warranted, some of which isn’t), policy makers recommend a high-carbohydrate intake by default.

The bigger question is whether or not this is a scientifically defensible position.

I’ll address this issue in more detail in Carbohydrate and Fat Controversies: Part 2