Improving insulin through diet: calories vs. carbs

In part three of Ben Bikman’s series, he looks at the effects of energy and hormones on insulin resistance and offers tips for building an insulin-friendly diet


Article highlights

  • Both low-calorie and low-carb diets can improve insulin resistance, but research shows lowering carbs has a greater positive impact on insulin sensitivity.
  • A low-carb diet led to 3x more improvement in an insulin resistance score compared to an equally low-calorie but higher-carb diet in one study.
  • People with higher baseline insulin saw significant drops in insulin on a low-carb but not low-fat diet, indicating improved insulin sensitivity.
  • To lower carbs, avoid added sugars, processed foods, and liquid calories, while focusing on protein, natural fats, fermented foods, vegetables, and other whole foods.
  • Improving insulin sensitivity involves diet quality overall, including sufficient protein, healthy fats, micronutrients, and lifestyle factors like exercise, sleep, and stress reduction.

In my last two articles, I discussed the origins and consequences of insulin resistance. It’s associated with nearly all chronic conditions, such as heart disease, diabetes, infertility, and Alzheimer’s disease. Half of all U.S. adults are known to have it, and over 80% may have it. It’s a health disorder we all want to avoid. Thankfully, insulin resistance and so many of the conditions that stem from it are readily reversible. The smartest strategy for doing that is changing our diet: Ultimately, the food we eat is either the culprit or the cure.

“Thankfully, insulin resistance and so many of the conditions that stem from it are readily reversible. The smartest strategy for doing that is changing our diet: Ultimately, the food we eat is either the culprit or the cure.”

At least to some degree, every dietary strategy focuses on either energy (calories) or hormones (insulin) and how to lower one or the other. Both strategies have merit because they address two fundamental causes of insulin resistance: too many calories and chronically elevated insulin. Unfortunately, the modern diet brings both, including hypercaloric, irresistible, insulin-spiking foods. So cutting either the energy or the insulin (by lowering carbohydrate intake) will yield positive results. But increasing research demonstrates that a carb-targeting approach is more effective at reversing insulin resistance. Here, we look at the case for both.

(We should note that your diet paradigm is just one factor that can affect insulin resistance. Many other aspects of nutrition play a role, including micronutrients, essential fatty acids [Omega-3 instead of Omega-6], dietary impact on the microbiome, and fiber, as do lifestyle factors like exercise and sleep.)

Low-Calorie Diet

“Lowering energy in the diet” is a clever euphemism for cutting calories. This has been the dominant strategy for decades, and it’s not without merit. There’s little doubt that most people (certainly those with insulin resistance) eat too many calories. While attempting to account for every calorie in and out is fruitless to the point of silly, scrutinizing energy is worthwhile. When eating fewer calories, the body has to use more stored energy, including fat from adipose tissue and glycogen from the liver.

Several human studies demonstrate improvement in insulin resistance with low-fat, low-calorie diets. Note that “low-fat” and “low-calorie,” while distinct ideas, are often used synonymously: If you’re seeking to cut calories, avoiding the most calorically dense of the macronutrients is the most logical and effective point of attack.

(In research that finds improved insulin resistance with a low-calorie diet, one detail to note is the “control group,” the group not eating the low-fat, low-calorie diet, which is serving as the baseline. Often in these studies, the control group is the standard American diet. This leads some to suspect that any dietary change from the norm may be beneficial—including, say, a diet that focuses only on potatoes.)

Unfortunately, there is a potential drawback to the low-fat approach. By pointing the finger at fat while embracing carbohydrates, we risk the person with insulin resistance raising their insulin levels, making their insulin resistance worse. A seminal 1987 study by the legendary diabetes scientist Gerald Reaven showed just this effect. Dr. Reaven had a group of insulin-resistant study subjects follow the low-fat diet proscribed by the American Diabetes Association, which encouraged roughly 60% of calories from carbohydrates. Unfortunately, the subjects’ triglyceride-to-HDL ratio—an indicator of insulin resistance—got worse, leading Reaven to conclude that it seemed “prudent to avoid the use of low-fat, high-carbohydrate diets.”

On the extreme end of “low-energy” interventions is surgical weight loss, such as gastric bypass surgery. These essentially force a low-calorie diet by severely restricting stomach volume. The insulin-sensitizing results are staggering—profoundly insulin-resistant individuals (with frank Type 2 diabetes) become wholly insulin sensitive in days—but this is a severe solution.

Low-Carbohydrate Diet

The approach that targets insulin by prioritizing fewer carbohydrates is far less popular than the low-energy paradigm today. Still, the growing body of evidence of its efficacy will undoubtedly tip the scale in its favor in the coming years. Not only does this diet increase insulin sensitivity, but it also does so at least as well and often better than the calorie-targeted approach.

In one study, subjects were separated into two dietary groups, low-fat and low-carbohydrate, for 12 weeks. The insulin resistance score improved by roughly 15% in the low-fat group, certainly an improvement. But the low-carbohydrate group saw a more than 50% reduction in insulin resistance. A key point: the two diets were isocaloric, meaning subjects took in the same amount of energy. Still, the insulin-lowering approach resulted in a three-fold greater improvement. This result certainly challenges the energy-centric paradigm.

Another study provided a spectrum of diets, with low-fat and low-carbohydrate diets on the ends with a middle-range “Mediterranean diet” in the middle. Once again, the breakdown of macronutrients, not the energy content, proved to be the difference: the most significant change in insulin resistance occurred in the lowest-carbohydrate group, with the highest-carbohydrate (lowest-fat) group having the least effect.

A secondary analysis of another weight-loss study revealed a powerful conclusion: The degree to which a person favorably responds to a low-carbohydrate diet (metabolically speaking) is tied to their initial fasting insulin, a strong indicator of their insulin sensitivity status. People who were already insulin-sensitive saw little change in fasting insulin levels on either a low-fat or low-carbohydrate diet. However, people with higher fasting insulin had no response to the low-fat diet—insulin levels didn’t budge, suggesting no change in insulin sensitivity. The low-carbohydrate diet, in contrast, lowered insulin significantly, indicating a marked improvement in insulin sensitivity.

What Does This Mean for You?

Even if you’re not trying to lose weight or battle insulin resistance, there is value in the low-insulin diet approach. Reducing overall insulin helps maintain insulin sensitivity, helping to keep you from tipping into a metabolically unhealthy state. Here are some simple steps you can take.

  1. Control carbohydrates: Of the three macronutrients (protein, fat, carbohydrates), carbs not only cover the broadest spectrum of foods but are also the biggest insulin offenders. In general, a carbohydrate will spike insulin more than anything else. But not all carbohydrates are created equal—here are some basic carb principles:
    • Don’t be so sweet. Sugar induces a considerable insulin spike. Limit sugar-heavy treats and watch out for hidden sugar in everyday foods, including sauces, dressings, ketchup, and peanut butter.
    • Go natural. The more natural the carbohydrate, the better. Carbs that come from processed foods are more likely to have a negative effect. A good rule: If it comes in a bag or a box with a barcode, it’s likely a carbohydrate to avoid.
    • Don’t drink your carbohydrates. There is a big difference in insulin response between drinking a fruit and eating the same fruit. When we remove or alter a fruit’s fiber, we absorb the fruit’s sugar more quickly. The presence of natural fruit fiber dramatically reduces the insulin response to the fruit.
    • Get fermented. In fermented foods such as yogurt, sauerkraut, or sourdough, the bacteria do some glucose digestion for us, lowering the glucose that gets into the blood.
  2. Prioritize protein: If we keep carbohydrate consumption and blood glucose low, we’ll typically have little or no insulin response to dietary protein. In contrast, high carb consumption and elevated blood glucose can lead to a substantial insulin response to protein. To optimize muscle and bone growth and exercise recovery, aim to get 1 to 1.5 grams of protein per kilogram of body weight. If you’re older, you need to be on the higher end of this. We become progressively less capable of changing dietary protein into muscle protein as we age. Lastly, be careful with cured meats, including sausages and jerky, which often include a lot of sugar.
  3. Don’t fear fat: Dietary fat has little effect on insulin. It’s a useful nutrient that can nourish your body while not contributing to an insulin load. Don’t feel compelled to add fat, but don’t worry about it, especially when it comes with protein (as nature intended).
  4. Remember the rest of a healthy diet and lifestyle. Many factors go into reducing the risk of insulin resistance. In addition to the steps above:
    • Aim for a balanced intake of micronutrients, including calcium, magnesium, B-vitamins, chromium, vanadium, zinc, carotenoids, and vitamin A
    • Avoid processed seed oils like soybean oil, which have damaging Omega-6 fatty acids.
    • Eat plenty of low-carbohydrate vegetables, such as cabbage, broccoli, cauliflower, and spinach.
    • Try to reduce stress.
    • Get plenty of exercise, including frequent, low-intensity movement like walking alongside more active workouts.
    • Prioritize sleep, which has a profound impact on metabolic health.