Understanding Food: Carbohydrates

Ah, carbohydrates. The new bad guy, right? The one who makes you decline those buttery dinner rolls and carrot cake?

Well, yes. Bad guys. Sort of. Not all the time.

Depends on you, your metabolism and activity level.

First, let’s explain what carbs are. In essence, they’re sugars, and sugars have the effect of raising insulin levels in your body. Excess insulin can also lead to rapid fat storage (and even disease) in sedentary and/or metabolically damaged individuals, which is where carbs get their bad name. That and the fact that the Standard American Diet (SAD) is massively, ridiculously heavy in processed carbohydrates.

Up First: Glucose

Glucose is a very common sugar found mostly in plant foods like fruits, veggies, grains and starches. It’s the basic sugar molecule found in a great deal of our food.

Unlike pure carnivores (like lions and some extremely cool dinosaurs), we humans male a digestive enzyme called amylase, which allows us to digest starch into glucose. We’re awesome that way.


Assuming you are not metabolically damaged, you digest starch and glucose pretty easily. It is only when your metabolism isn’t working up to snuff – usually caused by years of eating processed foods like refined grains, fructose and so-called “healthy” seed oils — that excess glucose is not properly digested and leads you to insulin resistance and diseases like diabetes. Problem is, glucose and foods that break down into glucose are abundant and cheap, and that’s why we’re seeing diabetes rates skyrocket and people say it’s a difficult cycle to escape.

So what to do? The range of glucose that different folks can tolerate varies massively. So, once again assuming you are not completely sedentary and are metabolically healthy, glucose may be consumed pretty liberally. However, many people today do have some form of metabolic dysfunction, and live a sedentary lifestyle. If this sounds like you, limit your glucose. Try aiming for no more than 150g of glucose (600 calories from glucose) per day.

Fructose: A Super Healthy Fruit Sugar, Right?

Well, if you believe food marketing, sure. If you believe science, not so much.

Fructose is a sugar found in fruits and vegetables. It’s a caloric content is the same as glucose (4 calories per gram), but what it does to your body chemically is a whole ‘nother story.

Says Harvard Health:

When fructose is joined to glucose, it makes sucrose. Sucrose is abundant in sugar cane, sugar beets, corn, and other plants. When extracted and refined, sucrose makes table sugar. In the 1800s and early 1900s, the average American took in about 15 grams of fructose (about half an ounce), mostly from eating fruits and vegetables. Today we average 55 grams per day (73 grams for adolescents). The increase in fructose intake is worrisome, says Lustig, because it suspiciously parallels increases in obesity, diabetes, and a new condition called nonalcoholic fatty liver disease that now affects up to one-third of Americans. (You can read more about nonalcoholic fatty liver disease in a Harvard Health Letter article.)

Virtually every cell in the body can use glucose for energy. In contrast, only liver cells break down fructose. What happens to fructose inside liver cells is complicated. One of the end products is triglyceride, a form of fat. Uric acid and free radicals are also formed.

None of this is good. Triglycerides can build up in liver cells and damage liver function. Triglycerides released into the bloodstream can contribute to the growth of fat-filled plaque inside artery walls. Free radicals (also called reactive oxygen species) can damage cell structures, enzymes, and even genes. Uric acid can turn off production of nitric oxide, a substance that helps protect artery walls from damage. Another effect of high fructose intake is insulin resistance, a precursor to diabetes.

So, bottom line: people without metabolic issues can handle small amounts of fructose (like a few small pieces of fruit) without problems. But on the scale that fructose is consumed here in the U.S. (everyone knows about the fight against high fructose corn syrup (HFCS) by now, right?), fructose is not your friend. Limit your intake.

So how on Earth can you eat carbs? Can you eat carbs?

Yes, you can. As Mark Sisson notes, try to stay under 150g of carbs per day. If you eat a diet full of processed foods, this will seem insanely tough. If you eat whole foods, fresh meats and lots of veggies and healthy fats, it’s imminently do-able. Keep your sugars more toward the glucose end, and limit fructose pretty significantly.

If you are active and/or an athlete, you will need to cycle carb levels based on training loads. But for the vast majority of us, keeping carbs around 150g/day is a huge step forward. It requires some new thinking about your diet, but that’s what this blog series is about, right?

Tags: , , , , , , Posted by

2 Responses

Leave a Reply

%d bloggers like this: