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  #1   ^
Old Sat, Dec-31-16, 06:59
teaser's Avatar
teaser teaser is offline
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Default A diet that induces obesity causes inactivity first

https://www.sciencedaily.com/releas...61229141901.htm

Quote:
Inactivity in obese mice linked to a decreased motivation to move






Quote:
Starting a regular program at the gym is a common New Year's resolution, but it's one that most people are unable to stick with for very long. Now a study done in mice is providing clues about one of the reasons why it may be hard for so many people to stick with an exercise program. The investigators found that in obese mice, physical inactivity results from altered dopamine receptors rather than excess body weight. The report appears in Cell Metabolism on December 29.

"We know that physical activity is linked to overall good health, but not much is known about why people or animals with obesity are less active," says the study's senior author Alexxai V. Kravitz, an investigator in the Diabetes, Endocrinology, and Obesity Branch at the National Institute of Diabetes and Digestive and Kidney Diseases -- part of the National Institutes of Health. "There's a common belief that obese animals don't move as much because carrying extra body weight is physically disabling. But our findings suggest that assumption doesn't explain the whole story."

Kravitz has a background in studying Parkinson's disease, and when he began conducting obesity research a few years ago, he was struck by similarities in behavior between obese mice and Parkinsonian mice. Based on that observation, he hypothesized that the reason the mice were inactive was due to dysfunction in their dopamine systems.

"Other studies have connected dopamine signaling defects to obesity, but most of them have looked at reward processing -- how animals feel when they eat different foods," Kravitz says. "We looked at something simpler: dopamine is critical for movement, and obesity is associated with a lack of movement. Can problems with dopamine signaling alone explain the inactivity?"

In the study, mice were fed either a standard or a high-fat diet for 18 weeks. Beginning in the second week, the mice on the unhealthy diet had higher body weight. By the fourth week, these mice spent less time moving and got around much more slowly when they did move. Surprisingly, the mice on high-fat diet moved less before they gained the majority of the weight, suggesting that the excess weight alone was not responsible for the reduced movements.

The investigators looked at six different components in the dopamine signaling pathway and found that the obese, inactive mice had deficits in the D2 dopamine receptor. "There are probably other factors involved as well, but the deficit in D2 is sufficient to explain the lack of activity," says Danielle Friend, first author and former NIDDK postdoctoral fellow.

The team also studied the connection between inactivity and weight gain, to determine if it was causative. By studying lean mice that were engineered to have the same defect in the D2 receptor, they found that those mice did not gain weight more readily on a high-fat diet, despite their lack of inactivity, suggesting that weight gain was compounded once the mice start moving less.

"In many cases, willpower is invoked as a way to modify behavior," Kravitz says. "But if we don't understand the underlying physical basis for that behavior, it's difficult to say that willpower alone can solve it."

He adds that if we begin to decipher the physiological causes for why people with obesity are less active, it may also help reduce some of the stigma that they face. Future research will focus on how unhealthy eating affects dopamine signaling. The researchers also plan to look at how quickly the mice recover to normal activity levels once they begin eating a healthy diet and losing weight.


http://www.sciencedirect.com/scienc...550413116305964

The study itself is full access.

I think some of this applies to lean "lazy" people as well. A healthy person isn't on a forced march, all gritted tooth and determination--moving is supposed to feel good, I don't think it's all a matter of character (unless we admit that much of what we call "character" is just how an underlying physiology manifests in a person's behaviour). And, not to rule out a little bit of self-imposed forced marching, but I think it will be more likely to be effective when the exercise itself promotes the sort of changes in brain physiology that promote activity--providing diet induced obesity animals with running wheels does help, perhaps by providing an activity that's a bit more fun than just scurrying around a cage. Similar to the thing with food, perhaps, where an obese animal will eat less of a low reward food like low fat chow. Obese mice have a higher threshold for sweet and fatty flavours--subtle foods become less enjoyable if they can't taste the light sweetness, something like an oreo is so blatantly sweet that an animal that's less sensitive to sweetness can still enjoy it.

http://www.sciencedirect.com/scienc...550413111003093

Quote:
Laboratory animals usually become relatively insulin resistant and obese. In this issue of Cell Metabolism, Cao et al. (2011) find that mice living in a complex environment are resistant to diet-induced obesity because they produce energy-dissipating brown fat cells within white fat depots, a process orchestrated by brain-derived neurotrophic factor.
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  #2   ^
Old Sat, Dec-31-16, 08:36
Liz53's Avatar
Liz53 Liz53 is offline
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Interesting. Does sugar and/or excess insulin have a negative effect on dopamine receptors?
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  #3   ^
Old Sat, Dec-31-16, 08:47
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WereBear WereBear is offline
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Quote:
Originally Posted by Liz53
Interesting. Does sugar and/or excess insulin have a negative effect on dopamine receptors?


Sugar has such strong effects on dopamine receptors that the brain downregulates; then it takes more sugar to get the same effect.
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  #4   ^
Old Sat, Dec-31-16, 09:44
Zei Zei is offline
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Quote:
"There's a common belief that obese animals don't move as much because carrying extra body weight is physically disabling. But our findings suggest that assumption doesn't explain the whole story."

If extra body weight were disabling, all those beefy gym rats and football guys who must weigh a ton more than less muscular people would therefore be disabled by their extra body weight, but they're obviously not. I've always thought the same thing goes for the argument that carrying extra pounds of fat is bad for the heart simply because of the extra blood vessels inside that fat that the heart must pump blood through. Muscle's got to have a lot of blood vessels supplying it, too, yet you never hear people complaining about how bad all the extra distance pumping through all that excess muscle must be for the heart. Or any complaints about stressing our hearts and being bad lifting iron in the gym compared to lifting our own bodies to move around if we're obese. We had one of those body fat scales that measures your lean (muscle, bone etc.) mass and I was amazed at the huge amount of sheer muscle of someone morbidly obese that tried the scale. Obese, yes, but hugely muscular underneath from the daily exercise of moving a heavy body around. So something else likely not about body heaviness/difficulty of moving heavy things is going on. And it sure can't help that when hormones are out of whack making you gain body fat that your body is partitioning needed fuel away from other working organs like muscles, heart and brain to the fat cells. Not surprised dopamine and who knows what else could be messed up under such conditions. I'm glad to see some researchers taking obesity scientifically seriously rather than the tired old bigoted insults of overeating and laziness that get hurled at heavy people.
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  #5   ^
Old Sat, Dec-31-16, 09:50
teaser's Avatar
teaser teaser is offline
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Plan: ketosis/IF
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One mostly undisputed observation is that if you get the sweetness just right, an animal will eat more of a chow--and that would probably contribute to the effects in this study.

The diet they called "high fat" vs. the control diet was also entirely purified--I don't know if it contained that much more sucrose, but where the control diet had ingredients like soy meal and hulled corn, the experimental diet had sucrose, soy oil, vitamin and mineral mixes, maltodextrin, etc.
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  #6   ^
Old Sat, Dec-31-16, 11:22
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Meme#1 Meme#1 is offline
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Plan: Atkins DANDR
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Most of the livestock feed uses Molasses which is high in protein.

In the winter we also feed big tubs of molasses mixture so they will produce internal heat for warmth.

But the livestock aren't lazy after that.......
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