The Latest on Carbs, Fat and Weight Loss

by | Jan 29, 2009

A study published last week in the journal Obesity may make you question whether you really want to rely on the Atkins or South Beach diets to reach your New Year’s Resolution goals.

It is widely believed that low-carbohydrate, high-fat diets support weight loss in most individuals and indeed, there is a good amount of research to back this claim. Despite this, few studies have examined the after effects of a low-carb diet, particularly once normal eating is resumed.

In a new study, scientists had rats consume either a regular high-carb diet or a low-carb, high-fat diet for sixteen days. After this period the diets were switched and rats were maintained on the opposite diet for another sixteen days. Both diets included the same number of calories, so the only difference between the groups was the relative percentage of macronutrients.

As you might expect, while the rats were fed a low-carb, high-fat diet they lost weight compared to rats on a regular diet. Interestingly, however, despite this loss of body weight there was little to no loss of fat, and therefore the rats that lost weight had a relatively higher body fat percentage than the rats fed a normal diet.

The low-carb rats also had lower energy expenditure (exercise and calorie burning) than rats on a normal diet, and the decrease persisted even when the animals were returned to a normal diet. This is consistent with reports of exhaustion in humans undergoing very low-carb diet regimens.

Furthermore, animals that were temporarily put on a low-carb diet regained more weight than animals that were never fed a low-carb diet. This suggests that short term exposure to a low-carb diet increases risk of weight gain compared to no dieting.

Uh oh.

According to this research it is possible that a low-carb diet may actually cause you to gain weight in the long run. How very unfortunate.

But while these results are compelling, do not go stocking up on pasta just yet. First remember that these are rats, not humans. The way scientists change the composition of a rat’s diet is by giving them different pellets of bizarre lab food with various proportions of “nutrients.” This is not the way humans eat (assuming you don’t spend too much time in GNC), nor can it ever reflect a healthy human diet. It would be great if they could put the rats on a diet of seasonal fruits and vegetables, whole grains, legumes and fatty fish, but that is not the way animal research works. This is something to keep in mind whenever you hear about nutrition studies.

Also, nutrition research using rodents rarely distinguishes between the qualities of different macronutrients. For example, did the “high-fat” diet contain mostly saturated fat, trans fat, monounsaturated fats, polyunsaturated fats or all of the above? A similar question can be asked about the quality of carbohydrates, but it is difficult to imagine high-quality carbohydrates coming in pellet form. A huge body of scientific literature suggests that the quality of different macronutrients is far more important to health and weight than relative proportions of refined macronutrients.

Protein is another question mark in this study, which the authors acknowledge. The low-carb diet they used was not high in protein like a typical Atkins style diet. However, their findings were similar to studies that did use higher protein content and their animals were fed sufficient protein to maintain normal body growth, so the effect of protein on their findings is likely to be small. Their goal was to examine the effect of extreme carbohydrate restriction, and this was accomplished.

Regardless of this study’s imperfections, the results shine an interesting light on our current understanding of how relative proportions of dietary macronutrients effect body composition, long-term body weight and metabolism.

Have you experienced weight gain after going off a low-carb diet?

UPDATE: This article is also available at Synapse.

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14 Responses to “The Latest on Carbs, Fat and Weight Loss”

  1. Matt Shook says:

    I’ve never tried a temporary (or fad) diet to lose weight, but the low-carb high-fat/high-protein diets always seemed like a bad idea. I talked with a doctor about low-carb diets once, and he thought they were dangerous…basically because carbs are the primary source of energy (essential for active people). He also mentioned that carbs are essential for ones diet for proper brain function…

  2. MizFit says:

    man there is so much debate on this. Im not low carb (I am lowlow processed white though) and the ultra low carbers (atkins to primal diet) think that we are created to run far better with so little carbohydrates that Im CERTAIN I couldnt even think straight.I guess to each her own huh?Ill keep my grains :)Miz.

  3. Darya Pino says:

    @MattIt’s true, your brain can only use glucose for energy. But if you are in ketosis (the Atkins goal) your body will make blood glucose out of fat. What really scares me though is all the evidence that animal protein promotes cancer. See the China Study book on my sidebar for details.—–@MizFitI’m with you. I virtually never eat processed white, unless it directly descended from heaven into my mouth (i.e. Tartine bakery).The science supporting both health and weight loss benefits of intact whole grain consumption is undeniable, so it always makes me laugh that some people are so against it.

  4. Anonymous says:

    Those rats are soooo cute!

  5. Matt Shook says:

    @DaryaI may be wrong, but doesn’t the state of ketosis put a lot of stress on the liver? That would seem a very counter-productive if your goal was better health…but I guess Atkins fans solely desire weight-loss.Wow, a possible link between animal protein and cancer? That’s big news…sounds like a good time to become an herbivore, or an extremely selective omnivore! I added The China Study to my queue when you recommended it to me. I should be able to start delving into it within two weeks time.

  6. Matt Shook says:

    Oh, and speaking of weight-loss…just read an interesting article regarding the benefits of almonds, particularly when sprouted. I’ve been eating them with my medjool dates, but I’m going to try sprouting some tomorrow…

  7. Karin says:

    First of all, those rats are not cute. No rats are cute, not as long as they have those beady eyes and wretched squeak. Secondly, this was a great article- You didn’t go into the mechanism much though, I want to know why changing percentages of macronutrients have such an effect.

  8. Darya Pino says:

    @MattTotally agree. Ketosis probably not ideal for the liver, and Atkins is more about weight loss than health. I’ve done the Atkins diet. Funny thing is, I lost more weight and became comfortable in my skin when I ditched the diet idea and embraced the health idea. Win win. Woohoo!I am still reading the China Study, but I image I will do a mini-review when I’m finished if I find it thoroughly convincing. So far it is very intriguing.That almond article is great reading too. I eat TONS of almonds, as my Twitter followers already know. Maybe that is why my body fat is so low :)—–@anon @karinI think the rats are cute, but mice are cuter.As for the mechanism, they actually did address it in the paper. I always worry about nerding out too much for you guys, but then I get questions about about the biological mechanism and I think, “My readers are smart!!”Anyway, apparently the low-carb diet was associated with lower levels of certain growth hormones that are correlated with fitness levels, particularly growth hormone and IGF-1 (which I assume is insulin-like growth factor 1–for some reason they never specify). The hypotheses is that lower levels of these hormones reduce muscles mass and lower metabolism.Hope this helps!

  9. Matt Shook says:

    @DaryaYou ditched the diet idea and embraced the health idea…and then blogged about it to help others. I’d call that a win-win-win.I still believe I’d be a terrible twitterer (?!) or TwEater…so I’m holding out. Almonds are awesome…tried sprouting some today…and they turned out great. Next I want to track down some raw Marcona almonds, which apparently are at the precipice of almond-dom.

  10. Scott says:

    I am suprised that studies/news like this doesn’t get more airtime on primetime channels/stations- Just think back a few years ago how much the Atkins diet and South beach was hyped; now there is pretty solid evidence coming out that in addition to the immediate health risks, there is a positive correlation to weight re-gaining in people who use these diets. I rather take my chances with bariatric surgery; there is an obvious risk, but the weight loss is permanent and guaranteed.

  11. Michelle says:

    Talk about The China Study makes me excited 🙂 What a great book! I’ve heard people poke holes in the study but for me it speaks volumes. Everyone, read it!

  12. Healthyliving says:

    It is weird and sad to even see diets like these; all fad diets are the same, in that you’re supposed to radically change your normal eating habit for something totally wacko. Japanese Bananas, anyone? Just another sign of how desperate everyone is to be healthy and look good, and how they are willing to completely forgo reason to do it.

  13. Matt Shook says:

    After reading this article I immediately thought of The China Study commentary here…gotta move that one up the queue!

  14. Andy says:

    Hey! I love white rates…. it looks so cute.weight loss pills

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