You Don’t Have a Carbohydrate Problem: It’s Your Fat Metabolism

Suzie Glassman

How impaired fat metabolism leads to insulin resistance and what you can do about it

How does a doctor determine if you’re at risk for or have type 2 diabetes? The most popular way is through a glycated hemoglobin (A1C) test. This blood test indicates your average blood sugar level for the past two to three months. The keywords are blood sugar.

What do you think when you hear those two words? Most people will say carbohydrates and refined sugar. Type 2 diabetes mellitus (T2DM) must be from a combination of things like too many donuts, sodas, sugary desserts, and fattening carbohydrates. While, yes, eating far too much of these foods will put you at risk, that’s not the end of the story.

While doctors use blood sugar to diagnose the illness, high blood sugar is merely a symptom. What’s causing your blood sugar to rise in the first place is the problem. Most people believe it’s a carbohydrate/sugar problem (and it is to an extent), but it turns out people with insulin resistance and/or T2DM also have a fat metabolism issue.

If I’ve lost you, stick with me. I’ll explain how people with insulin resistance burn carbs for fuel most of the time and how that contributes to weight gain and high blood sugar.

What is Insulin Resistance

Here is a quick overview of how insulin resistance develops.

  1. When you eat food, digestible carbohydrates are broken down to sugar, which enters the bloodstream.
  2. Your pancreas pumps insulin to get the blood sugar out of your bloodstream and into cells.
  3. In some cases, the cells stop letting insulin in. It’s as if insulin is knocking on the door, but the cells aren’t responding. Then, insulin has to knock louder and louder (meaning the pancreas makes more insulin to get to the cells to respond).
  4. Eventually, blood sugar rises to an unhealthy level.

The CDC explains that a lot of blood sugar in the bloodstream is very damaging to the body and needs to be moved into cells as soon as possible. There’s lots of insulin, too, telling the liver and muscles to store blood sugar. When they’re full, the liver sends the excess blood sugar to fat cells to be stored as body fat.

This sequence of events can lead to weight gain and impaired metabolism.

Metabolism and Resting Energy Expenditure

The role of metabolism is to break down food into energy for our cells. Of course, the food we eat is made up of carbohydrates, fats, and proteins. These macronutrients are then broken down into their simplest forms (glucose, fatty acids, and amino acids) during digestion.

Once broken down, these nutrients are either used right away for energy or stored for later use. Our primary energy source comes from adenosine triphosphate (ATP), the immediate useable form of chemical energy. But our supply of ATP is limited, so the body constantly resynthesizes it through one of three energy systems:

  1. Phosphagen (immediate source)
  2. Anaerobic (uses carbohydrates)
  3. Aerobic (uses either carbohydrate or fat)

We primarily use our aerobic system for all but high-intensity efforts. A healthy individual will burn mostly fat at rest and low-intensity work and then transition to carbs as the work becomes more anaerobic. The ability to switch fuel systems easily describes someone who is metabolically flexible.

To determine what fuel source your body is using, scientists use a test that measures your resting energy expenditure (RER). The test determines the ratio of carbon dioxide production to oxygen consumption. The result reflects how much carbs to fat you’re burning — .7 means you’re burning all fat, and 1.0 means you’re burning all carbs.

A Diabetes and Metabolism study shows individuals who have impaired metabolism actually have a higher carb-to-fat oxidation ratio, meaning they are burning more carbs at rest.

Brad Dieter, Ph.D., writes,

Not only is their baseline metabolism of fat impaired, but their ability to utilize fat during exercise is also impaired. Individuals with T2DM rely more heavily on carbohydrates than fat at virtually all exercise levels compared to their lean and healthy counterparts.

The research showed during four six-minute submaximal steady-state workloads, the lean person used about 55% fat and 45% carbohydrate while the obese individual used almost exclusively carbohydrates.

Dieter notes,

And it is not because there is not enough fat around. They have high levels of free fatty acids in the blood and intramuscular fat; they have a problem in turning that fat into usable energy.

Remember how too much blood sugar ends up as stored body fat? Now, you can’t burn off that body fat if your body is only using carbs for energy. At this point, you’re metabolically inflexible and much more likely to become insulin resistant.

The Issue With Carbohydrate Metabolism

Okay, so why are people who are at risk for or have T2DM told not to eat carbohydrates if they have no problem metabolizing them? The short answer is because carbohydrates are the first step in raising blood sugar.

Picture a bathtub. Eating carbohydrates turns on the faucet, and water (insulin) begins to flow. If there’s no insulin resistance, the drain is open, and water drains out at about the same rate as it’s coming in — there’s no risk the tub will overflow.

Shut or clog the drain or turn the faucet on so fast the drain can’t keep up (insulin resistance) and all of a sudden, you’ve got a mess to clean up. Limiting carbohydrates turns off the faucet (an important first step). The drain isn’t working correctly, but at least the tub’s not overflowing.

What scientists have demonstrated in recent years is that the problem isn’t with the faucet (carbohydrates themselves) or the tub — it’s with the drain. Individuals with T2DM have trouble transporting glucose into cells (glucose disposal). There’s good news, though. There are steps you can take to open the drain.

How to Unclog the Drain

Perhaps the simplest way to get the water moving out of the tub (blood sugar into cells) is to start exercising. I’m not even talking about exercise with the goal of weight loss (although I’ll talk about that next).

The American Diabetes Association notes a single bout of moderate-intensity exercise can increase glucose uptake into your cells by at least 40%. The benefits diminish after 48 to 72 hours, so you have to keep exercising regularly. Even a brisk walk of 30 to 60 minutes most days of the week is enough to see a benefit.

Dieter explains,

Engaging in exercise results in an acute increase in glucose disposal, both independent of insulin action and therefore temporarily improves insulin resistance. Exercise also improves fat metabolism in those individuals with impaired fat metabolism. This is a critical point. People with impaired fat metabolism can increase their ability to oxidize (burn) fat much more rapidly when they exercise!

Translation: During exercise, your muscles begin to take in more glucose to replenish what’s lost (the drain pulls more water through it). This step allows your blood sugar to lower, and the tub doesn’t overflow.

The other side effect is you get better at burning fat because exercising (especially when insulin is low, like after a period of not eating) helps your body learn to use more fat for energy.

The second way to unclog the drain is to lose weight. Yes, a low carbohydrate diet can certainly help. Other diets can too. What’s most important is you make diet and lifestyle changes you can stick to permanently. Giving up soda, excess sugar, and refined carbohydrates are a great place to start. And always listen to your doctor regarding your health management.

A group of British researchers found you don’t have to lose drastic amounts of weight to improve your health. They found that weight loss of ≥10% in the first few years after diagnosis was strongly associated with remission of T2DM at five years. If you’re 200 pounds, that equates to 20 pounds of weight loss.


There’s no question worldwide incidence of T2DM continues to rise. In the years between 1980 and 2014, the number of individuals diagnosed quadrupled. Scientists' understanding of this complicated disease state continues to evolve with time.

What's more clear now is individuals who fall on the spectrum of pre-diabetes to T2DM most likely have a fat metabolism issue. When they can’t tap into stored body fat for energy, a cascade of issues arises, eventually leading to insulin resistance, which is a glucose disposal problem (clogged drain).

Keep in mind exercise and weight loss work like Drain-O to repair the broken system. If you don’t know where to start, simply lace up your shoes and go for a walk most days (anywhere between 30 and 60 minutes). Find a weight loss plan you can maintain — it doesn’t need to be drastic. Focus on losing 10% of your bodyweight first.

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I write about health and fitness with the goal to help you live a healthier, happier life.

Denver, CO

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