Nutrition and Prediabetes

As I mentioned in my previous post there is some fascinating and useful information in Dr. Michael Greger’s book How Not To Diet on the relation between what and how we eat and prediabetes. This topic is important to me because a good friend of mine was recently diagnosed with prediabetes, and has been making heroic efforts in her eating to address it without medication. Insulin resistance is the strongly related to prediabetes, which is chronically elevated blood sugar (glucose). Sometimes the two terms are used interchangeably. Another term is carbohydrate intolerance. As a last bit of terminology, insulin sensitivity is the opposite of insulin resistance. We want our cells to have high insulin sensitivity which is the same as low insulin resistance. High insulin sensitivity also means high carb tolerance. Prediabetes is diagnosed with an abnormally high reading on an hbA1c test, which indicates your average blood glucose level over the last couple of months.


So first the basics. When food is digested our blood glucose level goes up. This signals to the pancreas to secrete insulin, which prompts the muscles and liver to receive the energy. It also prompts the fat cells to stop releasing energy, since there are readily available calories that need to be cleared from the blood. Excess glucose in the blood has various harmful side effects so it’s important for this to happen in a timely manner. In addition, the response to the excess glucose is for the pancreas to pump out more insulin, leading to elevated insulin levels in the blood, which has its own harmful effects

Cells can become resistant to the effect of insulin, so that not enough sugar is taken out of the blood in response to a normal dose of insulin. Some authors make the analogy that the insulin lock no longer fits in the cells’ keyhole, but I prefer Dr Greger’s analogy of a clogged drain. So insulin resistance reduces the outflow of sugar from the blood. The inflow of sugar is controlled by the food we eat, specifically its glycemic load: how much and how quickly the blood sugar rises in response to a specific number of calories of food consumed.

Refined carbohydrates have the worst glycemic load, so cutting back on them is a good way to “turn down the tap” of sugar inflow. It may seem like a good idea to cut back on all carbs, but this is failing to distinguish between “bad” (high-glycemic load) and “good” (low-glycemic load) carbs. You don’t have to cut down on all carbs to reduce blood sugar levels, just bad carbs. Also, carbs are not the only foods that cause insulin spiking. For example, beef, which contains no carbs, has a surprisingly high insulin response.

While it is a good idea to “turn down the tap”, the major question I often don’t see addressed is “why is the drain clogged” and what can we do to unclog it? Why did my friend suddenly become insulin resistant in her 60s? Especially in her case, because she doesn’t check any of the obvious boxes: she is normal weight, physically active, and eats a healthier diet than the standard American diet.

Intramyocellular lipids and insulin resistance
From Dr Neal Barnard’s Ted Talk
“Tackling diabetes with a bold new dietary approach”

It is by now well established that the insulin resistance is strongly associated with excess accumulation of intramyocellular lipids, or fat stuck inside muscle cells, and many experts argue that this is in fact the cause of insulin resistance. We don’t want a cross-section of our muscles to look like a marbled steak. Elevated blood fat (lipid) levels lead to increased intramyocellular lipids. And what we eat affects our blood lipid levels. This makes eating a reduced-fat diet seem like a good idea, but high triglycerides means excessive fat in the bloodstream, which can be caused by other types of excess calories, and the recommendations to lower triglycerides include exercise, avoiding sugar and other refined carbs, and lowering saturated fat consumption.

This is kind of what I new going into reading How Not To Diet but I picked up a lot of new knowledge there. Here is a summary of the new stuff I learned:

  • “Those eating plant-based diets average significantly lower insulin levels and have less insulin resistance, even compared to nonvegetarians at the same body weight. In fact, those who eat meat have up to 50 percent higher insulin levels in their bloodstreams” [1-4]. Intervention studies showed significant improvement by putting patients with type II diabetes on a plant-based diet [5]. There is a good discussion about how effective a plant-based diet is in preventing and treating diabetes in Dr. Greger’s video “The Best Diet for Diabetes“,
  • Our gut bacteria play a big role in carb tolerance. Bifodobacteria are good gut bugs we want to have, and bifodogenic foods encourages their growth. Unfortunately, some people are intolerant of a type of foods call fodmaps, which is associated with irritable bowel symptom among other things. But a low-fodmap diet can lead to lower levels of bifodobacteria [6] So it seems those who are on a low fodmap diet need to work harder at eating other foods allowed on their diet that are associated with good gut bugs.
  • Berries improve insulin sensitivity, and consuming them along with other foods, even bad carbs, blunts the insulin response to them. Eating more berries can overall lead to lower insulin resistance [7].
  • “Adding just two teaspoons of vinegar to a high-glycemic meal (a bagel and juice) reduces the blood sugar spike by 23 percent… A meta-analysis of eleven such studies found that vinegar taken with a meal significantly improves both blood sugar and insulin responses, and it didn’t seem to matter what kind of vinegar was used” [8]. As to how this works:”The mystery was solved when a research team in Greece demonstrated that vinegar consumption improves the uptake of blood sugar by our muscles” [9].
  • This next tidbit gets back to the meal-timing suggestion in my previous post: We are significantly more insulin sensitive in the morning compared to the evening. So avoiding higher glycemic foods in the evening is especially important for blood sugar control [10].


The recommendations discussed above still hold: move more, eat less refined carbs, eat less saturated fat, eat more high fiber foods including fruits and veggies. In the light of the lower insulin resistance associated with plant-based eating. moving towards lower animal protein intake and higher plant protein (like more beans, less meat) also seems like a good idea. In addition, there are some tweaks like eating berries with your meals, eating more in the morning and less at night (especially avoiding higher glycemic foods at night), and adding vinegar to your meals (Dr. Greger had some suggestions about vinegar with breakfast, but I must admit I have not tried that step yet). And don’t forget to work on your stress: we tend to eat junkier foods when stressed out. Fun physical activities and meditation (sitting or in motion) both help.


  1. Valachovicová M, Krajcovicová-Kudlácková M, Blazícek P, Babinská K. No evidence of insulin resistance in normal weight vegetarians. A case control study. Eur J Nutr, 2006.
  2. Kuo CS, Lai NS, Ho LT, Lin CL. Insulin sensitivity in Chinese ovo-lactovegetarians compared with omnivores. Eur J Clin Nutr. 2004.
  3. Toth MJ, Poehlman ET. Sympathetic nervous system activity and resting metabolic rate in vegetarians. Metab Clin Exp. 1994
  4. Hung CJ, Huang PC, Li YH, Lu SC, Ho LT, Chou HF. Taiwanese vegetarians have higher insulin sensitivity than omnivores. Br J Nutr. 2006.
  5. Barnard, R, Jung, T, and Inkeles, S, “Diet and Exercise in the Treatment of NIDDM: The need for early emphasis”, Diabetes Care, 1994.
  6. Hill P, Muir JG, Gibson PR. Controversies and recent developments of the low-FODMAP diet. Gastroenterol Hepatol (N Y). 2017
  7. Törrönen R, Kolehmainen M, Sarkkinen E, Mykkänen H, Niskanen L. Postprandial glucose, insulin, and free fatty acid responses to sucrose consumed with blackcurrants and lingonberries in healthy women. Am J Clin Nutr. 2012
  8. Shishehbor F, Mansoori A, Shirani F. Vinegar consumption can attenuate postprandial glucose and insulin responses; a systematic review and meta-analysis of clinical trials. Diabetes Res Clin Pract. 2017
  9. Mitrou P, Petsiou E, Papakonstantinou E, et al. Vinegar consumption increases insulin-stimulated glucose uptake by the forearm muscle in humans with type 2 diabetes. J Diabetes Res. 2015
  10. Bo S, Fadda M, Castiglione A, et al. Is the timing of caloric intake associated with variation in diet-induced thermogenesis and in the metabolic pattern? A randomized cross-over study. Int J Obes (Lond). 2015

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