Why some people must restrict carbs
June 22, 2013 · by Prof. Grant Schofield · in metabolic dysfunction, nutrition, obesity, public health, weight loss ·
OK, I will start this by saying that this is a more academic piece about metabolic control in type 2 diabetics, and the ethics of feeding them low fat diets. It is a bit technical in places and deals directly with original research. Read on if you are interested!
The key message is that in my opinion, when you are insulin resistant, really the first option you should consider is restricting carbs. I hear a lot about “it’s the processed carbs, not the starchy veges that are the problem”, that “vegetarian and vegan approaches are good at reversing type 2 diabetes”, that “fibre solves everything” and so on.
Look, I agree that healthy humans can eat a wide variety of macro-nutrients that may contain plenty of carbs and nothing adverse will happen, but it’s likely that processed carbs will help metabolically well regulated healthy people into insulin resistance and a downward cycle of getting fatter and sicker. The mechanisms by which fructose (sucrose – table sugar is half fructose) work are being understood more clearly by modern science. The way fructose stirs up inflammation, blood lipids, liver fat deposition, addictive pathways in the mesolimbic system in the brain, and causes leptin resistance (the off switch hormone) are all important factors.
Once, or if, you become insulin resistant, I believe that macro-nutrient profiles are very important. Mainly, I am talking about restricting dietary carbs. Remember, if you are insulin resistant then you will have a problem getting dietary carbohydrate into your cells. The pancreas needs to produce more insulin to help do this. In the early stages of insulin resistance, all this means is you end up being hyperinsuliemic – having constantly high insulin – if you eat even moderate amounts of any dietary carbohydrate.
Hyperinsulinemia is known to have multiple direct and indirect effects on the body, making things significantly worse. Insulin is directly inflammatory. Insulin turns off fat oxidation and promotes fat storage and conversion of carbs into fat (de novo lipogenesis). Insulin probably blocks the hormone leptin in the brain (off switch not working again!). High insulin is directly implicated in many cancers, especially breast and prostate cancers. The list is growing all the time as we understand more about this essential hormone, which causes havoc when out of whack.
Interestingly, the treatment approach of most endocrinologists, dieticians and diabetes specialists is to advise those with insulin resistance to have a low fat, moderate protein, high fruit and vegetable diet. Taken correctly, and iso-calorically for weight maintenance, for even consistent small weight loss, this wil be a moderate or high carbohydrate diet. True, the carbs have some fibre and you could avoid all processed carbs. Nonetheless, it is overall carb load that is important here for the insulin resistant person.
Here’s the kicker – some of the “best” carbs recommended for these people by health professionals, because they are low glycemic index, don’t help. This is because these carbohydrates are absorbed slowly into the system; but because the insulin resistant person is so easily overwhelmed by even moderate carb loads, the result is day-long hyperinsulinemia. There’s plenty of evidence for this too.
The evidence comes, in the main, from feeding studies comparing normal metabolically functioning people, with type 2 diabetics.
Here are a few examples:
1. First, I have written about this before in less detail, the study with beans and glucose. The main thing about this paper is that it compares diabetics with healthy non-diabetic controls. This is very important to see the differential insulin response provoked by the same carb load. This study shows how the insulin responses to several types of beans are high and prolonged for Type 2 diabetics compared with controls.
2, This study in Diabetic Medicine in 1989 shows how rolled oat meals in diabetics result in massive hyperinsulinemia and hyperglycemia compared to the healthy controls after 3 hours. It seems to me that any of these meals are the last thing you would want to feed to a Type 2 diabetic.
Rasmussen et al (1989). Postprandial glucose and insulin responses to rolled oats ingested raw, cooked or as a mixture with raisins in normal subjects and type 2 diabetic patients.
Cooking and processing of food may account for differences in blood glucose and insulin responses to food with similar contents of carbohydrate, fat, and protein. The present study was carried out to see if short-term cooking of rolled oats caused an increase in blood glucose. Furthermore, we wanted to see if dried fruit could substitute for some of the starch without deterioration of the postprandial blood glucose response. We therefore compared the blood glucose and insulin responses to three isocaloric, carbohydrate equivalent meals in 11 normal subjects and 9 Type 2 diabetic patients. Meals composed either of raw rolled oats, oatmeal porridge or a mixture of raw rolled oats with raisins were served. In normal subjects, the three meals produced similar glucose (75 +/- 22, 51 +/- 16 and 71 +/- 23 (+/- SE) mmol l-1 180 min, respectively) and insulin response curves (3160 +/- 507, 2985 +/- 632 and 2775 +/- 398 mU l-1 180 min, respectively). Type 2 diabetic patients also showed similar postprandial blood glucose (515 +/- 95, 531 +/- 83 and 409 +/- 46 mmol l-1 180 min, respectively) and insulin (5121 +/- 850, 6434 +/- 927 and 6021 +/- 974 mU l-1 180 min, respectively) responses to the three meals. Thus, short-term cooking of rolled oats has no deleterious effect on blood glucose and insulin responses, and substitution of 25% of the starch meal with simple sugars (raisins) did not affect the blood glucose or insulin responses.
3. Here’s another paper in Diabetes Care from 1987. In this study they fed diabetics 50g of starch contained in various foods. The foods were neither isocaloric, nor matched for other marco-nutrients (see table). The insulin response was greater for many of the foods than predicted by the glucose response. There were no comparison controls though.
The glucose and insulin areas under the curve are shown below. A few comments – while the lentils and kidney beans provoked a lower peak glucose, the rise took longer and the response was still increasing at 2 hours. Second, the results show that all foods produced hyperinsulinemia for several hours afterwards.
4. And then this paper in Diabetes Care from 1998. Look at the insulin curve responses to three different meals below – a standard American meal, a low starch/high fibre meal, and a high starch meal. You’ll notice a few things. First, the subjects are hyperinsulinemic after all meals. Second, the low starch meal appears to do much better than the higher starch meal. This research is flawed because the macronutrient compositions of the two meals are different – so it’s not the carbs that define the different insulin responses. There are no healthy controls either – so who knows what the difference is between meals and insulin resistant/insulin sensitive subjects.
The “high starch” diet is 55% carbs, 15% protein, and 30% fat. The “low starch” meal is 43% carbs, 22% protein, and 34% fat. So we see here that people have better insulin responses on lower carb, higher protein, higher fat diets! Just reduce the carbs a bit more and you might have something that resembles a healthy diet for a Type 2 diabetic. Another example of poorly conducted research reaching the wrong conclusions about dietary carbs.
5. Finally, heres a paper in the Archives of Internal Medicine from 2005. The figure shows the day long insulin response of the same subjects (they are their own control) on a low carb diet. The low carb diet is ketogenic. To be fair, the diets are not isocaloric because the subject spontaneously ate less food, as is usual for a low carb diet. They were not restricted and ate to fullness though.
Take home message:
If you are insulin resistant, you are by definition carbohydrate intolerant. Conventional treatment is to reduce fat, eat less processed carbohydrate, but still at least a moderate carb diet. That will result in chronic hyperinsulinemia and make things worse. The best and most sustainable approach is to restrict carbs and to eat moderate protein with fat as needed to fill you up. You can achieve the same result on a vegan diet or a vegetarian diet, it doesn’t matter, although more difficult. I would hypothesize that any diet in which the symptoms of diabetes are reversed is a carb restricted diet, whether it be through carb retsriction alone or an overall very low calorie diet.
Call to action? Understanding that dietary carbs affect some people very negatively is very important but not understood at all by mainstream medicine. Start telling your doctor about this! Pass on this blog, email people, get on Facebook or Twitter – do what you can. This will be a ground up movement in changing public health nutrition.