February 15, 2012

Nutritional biochemistry

How can carbohydrate restriction be healthy if it means limiting “natural foods” like fruits and vegetables?

Read Time 9 minutes

This week I’d like to tackle one of the most important questions that I get asked.  However, before getting to the question, I think it’s worth investing a few minutes to frame this discussion around a theme tightly linked to it — sugar.

If you’ve been following the nutrition news lately, you may have noticed that Dr. Rob Lustig has made some headlines.  If you’ll recall, Dr. Lustig is arguably the world’s expert on fructose (i.e., fruit sugar) metabolism, and I included a link to his now-gone-viral YouTube video on fructose toxicity from 2+ years ago in my post, Sugar 101.  In the February 2nd issue of the journal Nature, Dr. Lustig and his two colleagues make the following case:

  1. Sugar consumption is linked to the dramatic rise in obesity, diabetes, cancer, heart disease, and Alzheimer’s disease (i.e., the diseases that cluster around metabolic syndrome).  Effectively, sugar speeds up our aging process.
  2. The metabolic effect of sugar, and fructose in particular (fructose makes up half of sugar – sucrose is 50% glucose, 50% fructose; HFCS is 45% glucose, 55% fructose), is nearly identical to that of ethanol (drinking alcohol).
  3. As such, sugar should be regulated in a manner commensurate with the damage it causes.

Let me lay out a few facts.  First, our consumption of sugar is increasing at a staggering rate.  We consume, on average, about four times the amount of sugar today that we did 40 years ago, even though our consumption of sucrose (the white crystals) is going down.  How, you ask?  Because we have more than made up for it with the ubiquitous addition of high fructose corn syrup (HFCS) to darn near everything we eat (e.g., cereal, pasta sauce, salad dressing, virtually every form of “low-fat” food out there, condiments).   Remember the “Peter Principle” – when you see “low fat,” run the other way, as it is almost synonymous with “high sugar.”

The figure, below, from the Nature paper shows the amount of sugar (excluding fruit) that each country produces, in per capita figures.  If you factor in fruit, obviously the numbers are much greater.  A quick glance at this figure shows that (excluding fruit), the U.S. is the reigning undisputed champion of sugar production at over 600 calories per person per day, which means over 175 gm of sugar per person per day, (excluding fruit and fruit juice).   To fully understand why we produce so much sugar requires a discussion beyond the scope of what I want to write about today, but I’m sure most of you already have a pretty good idea: economic incentives.

There’s another interesting observation that can’t help but poke you in the eye when looking at this figure.  How many times do you ask (or get asked), “Why do some cultures eat carbs like rice and not get the same diseases we do?”  A quick glance at China, for example, sheds some light on this.  They may eat rice, but they sure aren’t producing (or eating) much sugar, on average.  Furthermore, the distribution of sugar consumption within the country is wide.  In other words, while the few wealthy people do eat amounts of sugar approaching Western amounts (along with other simple refined grains), the vast majority of non-wealthy inhabitants do not.  So while some have asserted that animal products and fats are the clear culprits explaining the different disease patterns in Asia, they’re missing this important point:  Given the absence of mechanistic and evolutionary reasons why animal products and fats are bad for us, is it more likely that sugar consumption is the single biggest factor differentiating the state of disease across these populations?


Global sugar glut Nature Lustig paper figure
Image credit: Lustig et al., 2012 in Nature

So what’s the upshot of this graph?  Well, for starters we eat a lot of this sugar.  Second, we export it, too.  This wouldn’t be a problem, I guess, if sugar were not so harmful.   How harmful is sugar?  For a long reminder, read Sugar 101.  For a very quick (by proxy) explanation take a look at the following table, also from the Nature paper, and previously presented by Lustig.


Table 1_Lustig Nature paper
Image credit: Lustig et al., 2012 in Nature

This table shows, side-by-side, the health problems that occur with chronic ingestion of ethanol (i.e., drinking alcohol) and fructose.  [Remember: fructose is the sugar found in fruit and fruit juice, but it also makes up 50% of table sugar (i.e., sucrose) and 55% of HFCS.]

I think the figure speaks for itself and suggests that about two-thirds of the pathology that afflicts a heavy consumer of ethanol also afflicts a heavy consumer of fructose.   As Lustig points out, this should not be terribly surprising, given that we ferment ethanol from fructose.

Let’s summarize:

  1. We produce and eat more sugar than any other country on earth, and do so more than at any other time in history.
  2. Consuming sugar is not just “bad” because of the “empty calorie” hypothesis (i.e., the reason one should limit sugar is because the calories from sugar are not as valuable as those from, say, protein); it’s bad because sugar is a chronic toxin.

One last point before we jump in:  Before you angrily email me, or say awful things about me for daring to suggest that Michelle Obama and the USDA might be wrong in recommending we eat 5-6 servings of fruits and vegetables (many vegetables are full of fructose, too) per day, keep one thing in mind.  I am simply making a few points and you need to decide how you want to interpret them and make personal choices around them.  We are all genetically different, and therefore have a very different genetic predisposition in our sensitivities around these foods (and all foods in general).

There are some folks out there who can eat enormous amounts of sugar and experience very little ill effect.  My wife is the poster child for this phenotype – though she doesn’t any longer, she could eat unlimited amounts of sugar and not gain weight*.  Furthermore, as we age, we generally get less adept at processing sugar, and therefore with each passing year a “fixed dose” of sugar appears to cause greater and greater harm to an individual.

*Note that I only commented on the “weight” portion of her phenotype.  When my wife did reduce her sugar intake, she experienced many benefits in her health, perhaps most importantly, her improved cardiac disease risk profile measured by advanced lipid testing.

Here are the points with which I want to challenge you:

  1. Before you assert something is “natural,” be sure to understand what you mean by “natural.”
  2. Don’t be afraid to question the notion that all things “natural” must be healthy (and by extension, that all things “un-natural” are unhealthy).

Let’s address these points in order.

Point I: How do you define “natural?”

Most people assume the fruits and vegetables we eat are “natural,” but in reality fruits and vegetables of today bear little, if any, resemblance to their original form.  Let’s take corn as an example.  [I’m choosing corn because (i) it’s illustrative of the broad science and progression of agriculture, and (ii) I happen to read a lot about it, as I find the evolution of corn cultivation fascinating.]   Bear with me for a moment, as I tell this story.

7,000 years ago — a sliver of time on the evolutionary scale — corn as we know it today was a plant called teosinte.  Teosinte was about the size of your thumb and had a few (maybe 4 or 5) kernels.  Over the next few thousand years we began the shockingly quick (by evolutionary standards) process of “domesticating” this crop from its “natural” state into subsequent states of what we now refer to as maize.   By domestication I mean the process of successive selection of crops that had the most advantageous features for our needs.  Sort of like “domesticating” animals so they would cuddle up with us on the couch instead of trying to eat us.

How did the process of domestication work?  As an example, farmers selected teosinte crops which were larger, had more kernels, were more resistant to drought, and were more resistant to pests and predators.  This process went on, growing season after growing season, until about the period of time leading up to World War II and morphed teosinte into a very different looking crop.  Hence, the progeny crop, maize, looked very different from the parent crop, teosinte.   At that time, around WWII, the average farmer in the U.S. could grow about 18 bushels of corn per acre per year, though progress in yield increase had been stagnant for a few hundred years.

Around 1940, however, the productivity (i.e., the yield improvement) and morphology (i.e., the physical “look”) of corn growth began to change dramatically for two main reasons.  First, this change was driven by the introduction of technologies to make cultivation more efficient (e.g., crop rotation, use of fertilizer and pesticides, improved irrigation).  This was referred to as the “industrialization” of agriculture.  Roughly in parallel to this effort, advanced biologic techniques of active breeding (genetically crossing one plant with another so they could mix genes – the same things animals do when they mate) and mutagenesis (disrupting the genes of the crop, typically using chemicals or other agents, like radiation, to change the genes of crops) significantly increased the functional genetic diversity of the crops, year after year, further increasing yields and other desirable crop properties, such as cost of production.

Furthermore, in the last 20 years or so, the introduction of genetic modification (GM) has made maize even more robust and genetically fit.  Today U.S. farmers can grow nearly 200 bushels of corn per acre per year, up from less than 20 bushels per acres per year in 1940.   Below is a figure showing corn yield data from the National Agricultural Statistics Service, which shows the almost unrelenting productivity gains in corn cultivation over the past 70 years.  The world’s leading technology companies leading this charge (Monsanto, Pioneer, Syngenta) are projecting yields of 300 bushels per acre per year by 2030.  In other words, with each passing year, technology is making corn more and more robust, and therefore more and more distant from what is “natural.”


US corn yields for past 50 years

What about apples? Oranges? Strawberries? Peas? Carrots? It turns out the story I’ve told for corn is virtually identical for every “crop” we grow today, including all of our fruits, vegetables, and grains.  I know what some of you are thinking, “I only eat organic non-GM fruits and vegetables, so I’m ok, right?”  Unfortunately not.  Genetically modified (GM) plants and crops are different from non-GM plants and crops in small genetic ways that generally make them more resistant to pests.  But the hallmark differences between, say, teosinte and modern maize are 95% accounted for without the addition of genetic manipulations.  For the purpose of this discussion, genetically modified crops are a moot point.  In other words, what we grow and eat today, even if we buy “organic” or “non-GM” has absolutely no resemblance to what was “natural,” say, 10,000 years ago.

So the next time you bite into a Fuji apple half the size of your head (these used to be my absolute favorite things to eat, by the way, and I’d easily consume 3 or 4 per day), ask yourself what it has in common with the “apples” your ancestors ate.  The answer, not surprisingly, is very little.


Natural foods

Point 2: Who says everything “natural” is good for you?

The next point I’d like to address is dispelling the myth that all “natural” substances (notwithstanding the argument, above) are healthy.  Let’s examine the role of toxicity in natural things we ingest by first distinguishing between two types of toxicity: acute toxicity and chronic toxicity.  Simply speaking, acute toxins are toxins that can kill you quickly, if you are exposed to a single dose, or a series of repeated doses in a short period of time. Conversely, chronic toxins are toxins that don’t kill you from a single exposure, but over time multiple exposures can kill you.

While there is no shortage of “man-made” toxins in the world, you might be surprised to learn how many “natural” toxins exist, too.  Let’s examine a naturally occurring acute toxin, a naturally occurring chronic toxin, and a naturally occurring toxin that is both acute and chronic.   The figure (below) shows each.

  1. Perhaps the most singularly potent acute toxin on earth is a molecule called tetrodotoxin, or TTX.  Tetrodotoxin is a nerve toxin that blocks sodium channels in our cells.  TTX is so potent that less than 200 pounds of this compound would kill every person living in the United States. In other words, it’s about 10 times more potent that cyanide.  Here’s the catch: TTX is found in nature – it’s 100% natural.  It’s found in puffer fish, newts, toads, and several other sources.  Several people die each year from exposure to TTX when they unknowingly consume animals containing the toxin.
  2. Tobacco is also a naturally occurring substance.  Whether smoked or chewed, however, it has many forms of chronic toxicity, primarily related to its carcinogenic (i.e., cancer-causing) properties.  In other words, you won’t die from smoking one cigarette or chewing one pack of dip, but if you do it enough, you might.
  3. Finally, ethanol is both an acute and chronic toxic.  While acute toxicity is rare, it is possible to overdose on ethanol (toxicity in this case is usually related to respiratory depression – that is, you stop breathing).  More common, of course, is the chronic toxicity of ethanol, which is well understood and well-documented.  For a quick reminder, take a look at the table I showed earlier in this post from the Nature paper.


Natural toxins

So there you have it.  There are plenty of “natural” compounds on earth that are harmful.  I am not suggesting that eating a Fuji apple is as toxic as smoking a pack of cigarettes, but I am saying that once you begin to understand the metabolic pathways of fructose (there are about 25 grams of fructose in a large apple) you’ll see that an apple, just because it grows on a tree, is not actually “good for you,” even though it is supposedly “natural.”  For some people, eating 10 apples a day causes no harm.  For others, eating 1 apple a day causes harm.  The goal should be to figure out what your “toxic” dose is — and stay well below it.

If you’re reading this and wondering how much sugar you can eat, it’s a bit like asking how much can you drink or smoke.  It depends.   How genetically susceptible are you to the effects of these toxins?  What are you optimizing for — short-term pleasure or long-term health?  This is where we get into the idea of dose-response.  I will address this in a future post, but not right now, as it really deserves a post of its own.


Photo by julian mora on Unsplash

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  1. Dr Attia, it is not wise to bunch all sugar-containing foods together for they do not have the same impact. For instance, it is right to speak harshly against soda pop and abundant consumption of fruit juices because the amount of sugar involved with frequent consumption of large portions is devastating on the long run to our biological systems. Not so for fruit even though they contain sucrose. The reason is that when a person consumes fruit, they are ingesting about 90% water mixed in with proportionally very small amounts of sucrose. We have been conditioned from an evolutionary perspective to accommodate this kind of sugar ingestion. Medically, there is no evidence tagging fruit consumption with diabetes and obesity, but there is such a correlation with soda intake and the ingestion of all sweetened beverages. Important to keep this sugar issue in perspective. David Bissonnette RD, PhD

  2. Peter,
    For a vegetarian (I don’t consume eggs), what vegetables/fruits are acceptable as part of a keto diet?

  3. I really appreciate the kind of blog you post here. You share this information well to viral keep it doing great job. Eating natural foods may bring best effects to our body & health. So, I am very happy to read this nice post.

  4. Are these disease studies fructose v ethanol controlling for weight? If eating some apples and bananas help me lose weight (or even twinkies and soda, for the sake of argument), perhaps then the fructose doesn’t cause harm any more than losing the same amount of weight/maintaining the healthy weight with no fructose.

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