Saturday, October 2, 2010

Insulin Sensitivity Affects Weight Loss

Last time we looked at the possibility that genetics may determine whether a person is able to lose more weight on a low-carb diet or on a low-fat diet. The jury is still out on that.

However, two articles from 2005 suggest that insulin sensitivity may play an important role in whether low-carb diets or low-fat diets work better for weight loss for particular people. The first of these, Insulin sensitivity determines the effectiveness of dietary macronutrient composition on weight loss in obese women, was published in Obesity Research. The second, A low-glycemic load diet facilitates greater weight loss in overweight adults with high insulin secretion but not in overweight adults with low insulin secretion in the CALERIE trial was published in Diabetes Care. Both articles were short, sweet and to the point. And both concluded that if you're insulin-sensitive, you will probably do better on a low-fat calorie-restricted diet, but if you are insulin-resistant, you can expect better weight loss on a low-carb calorie-restricted diet.

Experimental Design
The two studies were quite similar to each other, as outlined in the table above. Subjects were randomized into high-carb/low-fat (HC/LF) and low-carb/high-fat (LC/HF) diet groups. In both cases, high-carb was defined as 60% of calories, while low-carb was defined as 40% of calories. Not a dramatic difference, but because all the food was provided for the participants, it was possible to be fairly certain of what the subjects had consumed. (The amount of study food eaten plus any additional food eaten was taken into account.) In all cases, participants received a restricted number of calories.

Insulin Resistance
The variable of interest in these studies was insulin resistance. In the Obesity Research study, insulin resistance was determined by measuring fasting insulin levels. Insulin-sensitive (IS) individuals were defined as those with a fasting insulin below 10 mU/L and insulin-resistant (IR) subjects were defined as those with a fasting insulin above 15 mU/L. Subjects with a fasting insulin between those two values were excluded from the study. In the Diabetes Care study, insulin resistance was determined by administration of a 75 gram oral glucose tolerance test. The subjects whose plasma insulin at 30 minutes post-glucose was less than 66 mU/L were termed low insulin secreters and those whose plasma insulin at 30 minutes was above 66 mU/L were termed high insulin secreters.

As expected, all groups lost a significant amount of weight. The findings are summarized in the two figures below. (I have modified both figures from their original forms to make it easier to compare them.)

The Obesity Research article stated that they expected a loss of approximately 1 kilogram of body weight for every 7300 deficit in calories. Therefore, their 16 week study should have produced a weight loss of at least of 6.1 kilograms, and this was indeed the case.

What was surprising was that two of the groups lost almost twice that amount of weight: the insulin-sensitive (IS) subjects who ate high-carb/low-fat (HC/LF) and the insulin-resistant (IR) subjects who ate low-carb/high-fat (LC/HF). A similar result is seen in the Diabetes Care article. All of those subjects lost an average 6 kilograms or more of body weight, but among the high insulin secreters, significantly more weight was lost when they followed a low-carb/high fat diet as compared with a high-carb/low-fat diet. Among low insulin secreters, there was a tendency to lose more weight with a high-carb/low-fat diet, but in this case the difference was not statistically significant.

Take-Home Lessons
It pains me to say it, but a low-carb/high-fat diet may not be the best weight loss diet for everybody. From these two studies, a person who is still insulin-sensitive could well find that a low-carb diet might actually be their worst choice. It would still work, but not as well as a low-fat/high-carb/calorie-restricted diet. On the other hand, for a person who is insulin-resistant (and if you're not insulin-resistant when you're young, you tend to get that way as you get older), a low-carb/high-fat/calorie-restricted diet appears to work the best. For whatever reason, if you follow the diet indicated by your insulin sensitivity, chances are good that you will not only lose the amount of weight predicted by the decrease in your caloric intake, but a few extra kilograms as well.


Jake said...

I would not call these diets low carb because they exceed 10% of calories from carbs. Once again researchers are scared to do a real low carb test because they might find that low carb is far superior.

I would also say that in America finding a overweight person with good insulin sensitivity would be a difficult task.

Alex said...

Such an awesome blog! :-) I love it -- great post! Interesting info; I agree that a low-carb/high-fat diet is not for everyone. I personally know someone that was once obese but lost more than half of his body weight by watching calorie intake instead of carb intake.


Psst: Come check out my charity blog:
Please become a follower! ;-)

3D Face Analysis said...

Stargazey, I like your open-mindedness! You admitted that low-carb may not be the best for everyone. Rather than rationalizing the study away like other low-carbers. Rather than saying that those people hadn't followed low-carb correctly.

I think low-carb is only for females who are trying to lose weight. Males shouldn't diet or eat low-carb because it depletes the muscles of glycogen. So if you are a male and you don't want to look like a sissy, then eat some carbs!

Low-carb isn't masculine in any way, except if you have diabetes. But even then, type 2 diabetes can be cured if you eat a very low PUFA diet. A diet low in iron. A nutrient-dense diet. And a diet low in pesticides, contaminants, and heavy metals. The half-life of PUFAs is two years, so it may take a few years to get rid of those toxins and PUFAs within the body.

Stargazey said...

Interesting comments. :-)

Hi, Jake! You're right about 40% carbs not being a low-carb diet. But there was still a difference in outcomes, and if that gets scientists thinking, it's a good thing.

Hi, alex trumpe and thanks for the compliment!

Hi Organism as a Whole! I'd never heard the claim about low-carb and manly-looking muscles. It's obviously impossible to carb-up when you're doing low-carb, but there are other benefits to low-carbing like low basal insulin, low triglycerides and high HDL. Do we want to limit those advantages to women only?

Mario Iwakura said...

Interesting! But...

Those studies restricted calories and all food was provided. But, in real world, what would be the outcomes? Everyone that follows a low carb/high fat diet know that this diet controls hungry much better than a low fat/high carb.

So, if someone is obese but not IR, what diet he/she would prefer and have more chance to succeed in the long run: one that make you thin kicker but hungry all the time, because it has to be restricted in calories, or another that also make you thin (even if it takes a little longer) but not hungry, since your calories is naturally restricted?

3D Face Analysis said...

Yes, I want to limit low-carb to women only. Since low-carb makes you eat less because of the satiating effect of fat, low-carb is equivalent to starving yourself. So I don't recommend low-carb to children either, because they need lots of Calories to help them grow. Forcing children to go low-carb doesn't make them eat the required Calories to grow.

In order for you to grow muscle, you must eat more food. So low-carb is equivalent to eliciting the starvation response. What happens when you starve? Cortisol will rise. You muscles will catabolize. So unless men want to look like wimps, then normal men shouldn't eat low-carb.

3D Face Analysis said...


I agree that low-carb makes you feel "full" with less Calories. But have you heard that many of low-carbers have carb and sugar cravings on their diet, even when they're "full"? So this means that they are still spending lots of effort in restricting Calories by controlling their carb cravings.

Stargazey said...

Organism as a Whole, do you possibly believe that carbs are the body's only source of energy?

As far as starvation on low-carb, the Kimkins Diet proved that it's possible, but that it takes quite a bit of willpower--much more than most people possess. Google "Kimkins Diet Scam" for more information than you ever wanted to know about this diet if you haven't heard of it.

Not every low-carber manages to reach their goal weight, and when they do, maintaining it is quite a challenge. Please read Jimmy Moore's Menus Blog for a real-life example, and check out the Maintainers section of Low Carb Friends for even more.

3D Face Analysis said...

Stargazey, I think low-carb is cute...for women. Low carb allows them to have greater satiety and therefore allows them to starve themselves and lose weight. Lose weight from fat loss and also muscle wasting.

I actually don't mind if women lose some muscle following low-carb. They will look weaker, but I don't mind.

Yes, yes, I will confess that I am a bit of a sadist—I like women who are weaker than me.

Stargazey, also, I think the picture from this post is cute—you know—the people wearing their socks and weighing themselves on the scale. I can tell from the picture that these people are very skinny. See how skinny their legs and feet are? Why are they still obsessed in losing weight? Are they anorexic?

And why are there three scales? One scale is just enough. Are they that obsessed with their weight, and they must check three different scales to be more accurate?

My point is that these studies are flawed because they don't distinguish between fat loss and lean tissue loss. And visceral fat gain.

Geoff said...

Calling a 40% carb diet "low carb" is beyond idiotic. Someone eating "low carb" at that level will eat more carbohydrate in a day than I will eat in some months. I would bet the farm that you put either of the test groups on a ketogenic diet and they lose weight at a substantially greater rate than any of the test groups listed.

David Isaak said...

I realize that I'm down in the archives somewhere, but still--

Organism as a Whole, I'm afraid what you're saying doesn't make sense. Higher-protein diets--which low-carb diets usually are--do a bette job of preserving muscle mass. There are many studies that show this.

In my own case, I lost 60 pounds low-carbing. But I actually lost 70pounds of fat, because I gained ten pounds of lean body mass.

Take a look at photos of some of the Paleo low-carbers out there. Some of them don't exactly look like "sissies."

MM said...


I followed this link you posted from carbsanity, and wow this was me. I did lose 20 pounds on low carb, but then I couldn't lose any more. I tried for 18 months and my weight would not budge. It was so frustrating! I had developed quite a carbophobia at that point, and it was difficult for me to start eating carbs again. However, once I did the weight started dropping. So, I guess this means I started out IR, but losing 20 pounds on low carb made me insulin sensitive again? It has certainly been an interesting journey. Thanks for posting this.

Stargazey said...

You're welcome, and thanks for coming over! I do hope you are insulin-sensitive once again. Because you're health conscious, I'm sure you will be careful, though, and check your fasting and postprandial glucose every week or so, just to be sure that the insulin resistance isn't sneaking back. Best wishes!

MM said...

Yes, I check my blood sugar all the time. I know I'm at risk for diabetes, and when I first started on the low carb diet my fasting was in the pre-diabetic range. However, now they're normal, 70s usually. That's why eating carbs again was so scary for me, but I'm starting to think that maybe a low carb diet isn't the best long term for diabetes. Anyway, there's been an ongoing "discussion" (war?) about this over on carbsanity. Not sure you want to start one of those over here too. :)

Stargazey said...

You're right, I don't want a war like that over here!

I've been re-reading Dr. Atkins' books lately and was struck by how many times he says "controlled carb," not low-carb. And of course he wasn't an advocate of very low carb at all. Because we're all different, maybe controlled carb is the way to go--not diving back into the chocolate cake and ice cream, but eating a controlled amount of healthy carbs and keeping a careful eye on the scale and on our blood sugar in case things start to go awry.

Drew Stearns said...

I did a little digging on these two articles:

First, neither report the composition of the weight lost (lean vs. fat tissue).

Second, in the Obesity Research article, there's a chart showing changes in metabolic parameters from the beginning to the end of the study:

As you can see, the absolute amount of weight lost roughly correlates with the relative drop in insulin (although, only 3 of the 4 test groups are statistically significant).

If decreased insulin levels are related to increased levels of physical activity (per the carbohydrate-hypothesis) then energy expenditure may have caused the difference in weight lost between groups.

The point is moot however, because we don't know the tissue composition of the weight lost, and physical activity generally causes body re-composition.

This is a good example of a study providing evidence for two opposed weightloss paradigms.

It's also a good example of why studies need to be more carefully constructed if we ever want to know the true mechanisms of fat deposition and mobilization.