Much of the discussion about nutrition these days on social media seems to take an “all-or-nothing” stance on carbohydrates. On one hand there are those who promote a plant-based diet that necessarily comes with a large amount of carbohydrate as grains, legumes (pulses) such as beans and lentils as well as carbohydrate-containing vegetables and fruit, and on the other hand there are those who eschew anything with the remotest amount of carbohydrate.
In politics, there are left-leaning ‘liberals’ and right-leaning ‘conservatives’, as well as those that hold a moderate position called “centrists“.
I am a centrist when it comes to my position regarding carbohydrates. In this article, I will elaborate on the following;
- Carbs are not evil or single-handedly responsible for the obesity epidemic or metabolic diseases. If that were the case, then the traditional diets of much of Asia and West Africa would have resulted in obesity and diabetes and they did not. It is the degree of processing of the carbohydrate-based foods that impacts the blood glucose and blood insulin response of carbohydrate-containing foods.
- Carbohydrate-based foods combined with fat in the same food ‘hijack’ the reward center of our brains (striatum), resulting in over-consumption.
- Carbohydrates are not essential macronutrients.
Part 1 – Degree of Processing of Carbohydrate-based Foods Impacts Blood Glucose and Insulin Response
Processing carbohydrate even in simple ways such as cooking or grinding means that more of the carbohydrate is available to the body to be digested. As pointed out in an earlier article which I will refer to throughout this section, when grains are cooked they become much more digestible – meaning that more of the nutrients in the grain is available to be absorbed. In the case of potatoes, there is double or triple the amount of energy (calories) available to the body when they are cooked versus when they are raw.
Mechanical processing, such pounding, grinding or pureeing are also forms of food processing which have an effect on how many nutrients are available to be digested. The nutrients available to the body when food is eaten raw and whole versus raw and pounded is significant.
Glucose Response – based on the amount of food processing
Mechanical processing of a food doesn’t change the amount of carbohydrate that is in it. That is, when 60 g of whole apple are compared with 60 g of pureed apple or 60 g of juiced apple, there are the same amount of carbohydrates in each and the Glycemic Index of these are similar, however when these foods are eaten the blood glucose response 90 minutes later is significantly different. As outlined in the earlier article, in healthy individuals, blood glucose level goes very high with the juiced apple and in response to the release of insulin, blood glucose then goes very low, below baseline. The response that we see with the juiced apple in healthy individuals is typical of what is seen with other forms of ultra-processed carbohydrates.
This is why it is preferable for metabolically healthy people to eat carbohydrate-based foods as whole, unprocessed foods with a minimum of disruption to the cell structure.
Insulin Response with Mechanical Processing
When healthy individuals eat grain-based meals, the plasma insulin response is inversely related to the particle size of the grain. That is whole, unprocessed grain releases less insulin than the same amount of cracked grain, which is still less than the same amount of course flour. The highest amount of insulin is released in response to eating the same amount of fine flour.
This increased insulin response of eating grains that are highly processed can drive chronic hyperinsulinemia (chronically high levels of insulin) that eventually results in insulin resistance; the beginning of the metabolic disease process.
It is for this reason that for metabolically healthy individuals, eating whole, unrefined grains is recommended.
Effect or Lack of Effect of Fiber
It is the lack of disruption to the cell structure of the grain that limits the insulin response and not the fiber content that makes the difference.
As mentioned in the earlier article (link above), studies have been done with bread where the fiber was added back in (such as in so-called “whole wheat bread” which is essentially white bread with added bran) and the insulin response was the same as with white bread, so it is not the amount of fiber in the grain that makes the difference, but the lack of disruption to the grain structure itself. I find it helpful to think of it in terms of ‘the fiber that counts is that which is part of the whole, undisrupted grain’. (Note: it is for this reason that I only factor “net carbs” for food whose fiber is in this undisrupted form. For all other products where fiber is added, I don’t deduct the fiber).
The disruption of the structure of the grain also has an adverse effect on GIP response (an incretin hormone released from the K-cells high up in the intestine that triggers the release of insulin). Bread made with flour (as opposed to whole, intact grains) results in a much larger and earlier plasma GIP response, which in turn results in a higher and earlier insulin response, than bread made with whole kernel grains, such as artisanal rye or wheat breads.
In metabolically healthy individuals, the eating of whole, intact minimally processed carbohydrate-containing food is preferable, as opposed to eating processed carbohydrate-containing foods (be it grains or fruit) with significant disruption to the cell structure.
Part II – Carbohydrate and Fat Combined
In nature, there are very few foods in the human diet that contain a combination of both carbohydrate and fat in substantial quantities. Human breast milk is one of those few natural foods, along with some nuts and seeds. When humans began drinking the milk of other mammals such as goats, sheep and cows, milk became one of those foods.
Also as outlined in a previous article foods with both fat and carbs together result in much more dopamine being released from the reward-center of our brain, called the striatum. Dopamine is the same neurotransmitter that is released during sex and that is involved in the addictive “runner’s high” familiar to athletes so this is a very powerful neurotransmitter.
It is believed that there are separate areas of the brain that evaluate carb-based foods and fat-based foods but when carbs and fat appear in the same food together, this results in what the researchers called a “supra-additive effect“. That is, both areas of the brain get activated at the same time, resulting in much more dopamine being released from the striatum and a much bigger feeling of “reward” being produced. This combination of carbs and fat in the same food is why we find foods such as French fries, donuts and potato chips irresistible and this powerful reward-system is why we’ll choose French fries over baked potato and why we have no difficulty wolfing back a few donuts, even when we’ve just eaten a meal.
This “supra-additive effect” on the pleasure center of our brain along with the fact that more insulin is released when both carbs and fat are eaten together helps explain the roots of the current obesity epidemic and the metabolic diseases such as Type 2 Diabetes that go along with it. The high rates of obesity seen more recently in places like China (as covered in this article) are due to the adoption of Western eating habits (refined, processed foods) that are notoriously high in both carbohydrates and fat.
When foods that are rich sources of carbohydrate are eaten it is best that foods that are also rich sources of fat are not eaten at the same time in order to avoid this supra-additive effect.
I do not believe that carbohydrate-based foods in and by themselves in metabolically healthy individuals are the underlying cause of obesity and metabolic disease. I believe that it is the (1) consumption of carbohydrate-based foods that have undergone some kind of food processing (grinding, milling, pureeing, etc) that has disrupted their cell structure and (2) the consumption of foods that combine both carbohydrate and fat in the same food that have driven both.
Part III – Carbohydrates are Not Essential Macronutrients
With all the arguing about eating more carbs or less carbs, it needs to be emphasized that carbohydrates are not essential nutrients. Yes, the body needs a certain amount of glucose for the brain, but the body can make this glucose from protein and fat through a process called gluconeogenesis.
This is not simply my opinion, but is stated by the Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein and Amino Acids (2005) on page 275;
“The lower limit of dietary carbohydrate compatible with life apparently is zero, provided that adequate amounts of protein and fat are consumed.
That is, there is no essential need for dietary carbohydrate provided there are adequate amounts of protein and fat provided in the diet.
The Recommended Dietary Allowance (RDA) for carbohydrate is set at 130 g / carbohydrate per day based on the average minimum amount of glucose utilized by the brain— however the body can manufacture this glucose from protein or fat. A well-designed low carbohydrate diet provides sufficient amounts of fat and protein such that the body can manufacture the glucose it needs.
Carbohydrate – to eat or not to eat
For Healthy Individuals
For those who are healthy and metabolically flexible, consumption of whole, unprocessed carbohydrate-containing foods such as whole grains, tubers, starchy vegetables such as peas, squash and corn and whole fruit are of no concern. Due to the ‘supra-additive’ effect of fats with carbohydrate, I recommend that when eating carbohydrate-based foods, to avoid foods that are a rich source of fat.
For Metabolically Unhealthy Individuals
As mentioned in the two previous articles related to the new Canada Food Guide (here and here), 88% of Americans are already metabolically unwell, with presumably a large percentage of Canadians as well.
That is, only 12% have metabolic health defined as;
- Waist Circumference: < 102 cm (40 inches) for men and 88 cm (34.5 inches) in women
- Systolic Blood Pressure: < 120 mmHG
- Diastolic Blood Pressure: < 80 mmHG
- Glucose: < 5.5 mmol/L (100 mg/dL)
- HbA1c: < 5.7%
- Triglycerides: < 1.7 mmol/l (< 150 mg/dL)
- HDL cholesterol: ≥ 1.00 mmol/L (≥40 mg/dL) in men and ≥ 1.30 mmol/L (50 mg/dl) in women
For the large majority who are metabolically unhealthy, knowing which carbohydrate-based food raise one’s blood glucose levels is important. Even if lab tests show one’s fasting blood glucose is still normal, blood glucose levels after eating carbohydrate may be quite abnormal, and even more significantly insulin levels may be as well. You can read more about that here. As mentioned previously in this article, these high insulin levels are what drives metabolic disease by driving insulin resistance.
Eating a low carbohydrate diet can be very helpful to lower blood glucose response and lower chronically high levels of insulin. Which carbohydrates can be tolerated and in what quantities varies considerably between people, but is easy to determine and I help people do this.
For those that already have Type 2 Diabetes, reducing carbohydrate intake for a considerable length of time will enable them to reduce their overall blood glucose and insulin response, which will help them reverse the symptoms of Diabetes as well as other metabolic diseases that often go along with it, such as high blood pressure and high triglycerides. In time, some carbohydrates may be able to be eaten again however the amount and type will vary between individuals.
Carbohydrates aren’t “evil”. In and by themselves, they don’t result in obesity or metabolic disease. It is the amount of food processing that carbohydrate-containing foods have undergone that results in cell-wall disruption that will determine how much of a glucose– or insulin-response they will cause. In metabolically healthy people, eating minimally processed whole grains, starchy vegetables and fruit without a source of fat is fine.
For those who are metabolically unhealthy, especially those who have a measurably abnormal glucose- or insulin-response, the amount of carbohydrate that can be tolerated is individual and will need to be determined.
For those who have Type 2 Diabetes and follow a low carbohydrate diet to reduce the symptoms of high blood sugar or metabolic diseases that often go along with it, eating the amount of tolerated carbohydrates as minimally processed ones, without a source of fat is also best.
There is no “one size fits all” diet that is suitable for everyone.
For metabolically healthy individuals, following the new Canada Food Guide and selecting carbohydrate sources using the above principles can provide people with a healthy diet. For those that are already metabolically unhealthy, I can help design a Meal Plan that will meet your energy and nutrient needs and that provides the amount of carbohydrate that you can tolerate. If you would like more information, please send me a note using the Contact Me form, above and I’ll be happy to reply soon.
To your good health!
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