Many of us find that low-carbohydrate (LC) diets work the best to control our blood glucose (BG) levels. Many of us also find that LC diets control our hunger as well, which is very important when you want to lose weight.
And although you can lose weight on various types of diets if you control your calorie intake, controlling your calorie intake can be difficult when you're ravenously hungry most of the day. That happened to me. I lost weight on a low-calorie, low-fat diet when I was diagnosed, but I was ravenous the whole day and finally decided I couldn't live with this for the rest of my life and gradually switched to a LC diet, and the hunger disappeared.
Some people don't feel ravenous on a low-fat diet, and for them any type of diet works for weight loss or simply for health maintenance. But there's evidence that people with insulin resistance, which means most of us as well as people with metabolic syndrome, often a precursor to type 2 diabetes, do better on LC diets. In fact, one paper suggests that doing better on a LC diet might be considered a definition of metabolic syndrome.
I think the key here is that when you have insulin resistance, your BG levels can go very high after eating carbs, and then they come down fairly fast until you have overt diabetes. And I think this rapidly falling BG level triggers hunger. It's logical. If your BG is falling fast, the body wants to correct it before you go low instead of waiting until you're low, when it would take 15 or 30 minutes to correct the low, and by that time you could already be alarmingly low.
When I did mini oral glucose tolerance tests (OGTTs), I found I got ravenous just after the peak BG level, as illustrated in Figure 6 in my book The First Year: Type 2 Diabetes. If you can avoid those peaks and rapid falls, your hunger should abate.
People without insulin resistance don't see this effect, because their BG levels don't usually go as high after eating.
Thus, for people with insulin resistance, LC diets are beneficial. However, one thing many people on LC diets don't realize is that when you're on a LC diet, you become more sensitive to carbs. This means that an amount of carbs that wouldn't make your BG levels go up much if you weren't on a LC diet can make them go up a lot if you're not.
The most extreme example of a LC diet is starvation, zero carbs as well as zero anything else. People who are starving will test diabetic on OGTTs even if they're not. So that's why when you take an OGTT, for example, if you're pregnant, they tell you to eat a lot of carbs for 2 or 3 days before the test.
Why is this true? One reason is that when you don't eat carbs, your body stops producing the enzymes that metabolize carbs so they can remain in your bloodstream longer. Another reason is that when glucose is in short supply, the body tries to conserve it to use in the brain, which does need some glucose. One way to do this is to increase insulin resistance in the muscles, which can get their energy from fat (and often prefer to).
But is this insulin resistance bad?
I don't think it is as long as you stick to the LC diet. In other words, if you decide a LC diet will work for you, don't eat doughnuts every Sunday or cake when you're invited out, because when you do, your BG levels will most likely go very high.
A paper published in 1989 illustrated some of this.
Unfortunately, although the paper is finally available online, the figures are not. But I tried to read the values from small graphs in the paper, which Kerin O'Dea, the first author, kindly sent me from Australia a few years ago, and put them into a graphing program.
What these researchers did was to put people with type 2 diabetes on 4 diets: high-carb high fiber, high-carb low fiber, LC high fat, and LC high protein. I'll ignore the high-carb low fiber as I think everyone now agrees that this isn't a good approach.
The high-fiber diet (diet 1) "consisted of unrefined cereals, such as wholemeal bread, pasta, brown rice, at least one serving of legumes per day, fruit and vegetables, non-fat dairy products, and very lean meat and fish." It was very low in fat (about 9% total fat).
The LC high-fat diet (diet 3) "was achieved by the use of full-cream dairy products, eggs, fatty meats, butter, margarine, and oil. Leafy vegetables were eaten in usual amounts, but cereals and fruits were restricted." It contained 20% carbohydrate, which would be about 65 to 77 g of carbohydrate (depending on whether or not you subtract fiber) on a 1500-calorie diet. So it was probably not ketogenic.
The LC high-protein diet (diet 4) was low in fat and carbohydrate and very low in fiber. The protein content of this diet was exceptionally high in order to keep the energy content equivalent to that in the other three diets. The calories were "derived predominantly from lean meat (beef, fish, chicken, and pork). Skim milk products were restricted to a combined total of 600 gm/day Leafy vegetables were eaten freely but starchy vegetables, cereals, and fruits were restricted."
Participants weighed and recorded what they ate, and much of the food was provided to them. The researchers did an OGTT on the participants and then repeated it after 14 days on each of the diets. They also measured BG when the participants were eating the test diets both before and after the 14 days. This is a step that is not often done. Researchers usually feed some diet and then measure some parameters at the end of, rather than during, the test period.
The first figure shows the response before and after 14 days of the high-fiber diet.
(Note: the results are presented as mmol/L. To convert to mg/dL, multiply by 18.) Clearly the subjects did better on an OGTT after the high-fiber diet. Figure 2 shows the results from the subjects on the LC high-fat diet. Instead of doing better, they did worse on an OGTT, as if their insulin resistance had increased. The subjects on the LC high-protein diet, like those on the high-fiber diet, did better on an OGTT after the diet (not shown here). It looks as if the decrease was not quite as much as with the high-fiber diet, but they started at a lower level (peaking at about 15 instead of 19). The peaks after the diets were about 15 on the high-fiber diet and about 14 on the high-protein diet.
(Note: In all cases, the Y axis, the vertical one, shows BG levels in mmol/L. I forgot to change the labels on the graphing program, and as there were technical problems involved in getting the graphs to display here, I didn't go back and start all over again.)