Sucrose substitution in prevention and reversal of the fall in metabolic rate accompanying hypocaloric diets
Hypocaloric diets cause a fall in resting metabolic rate that interferes with weight loss. To evaluate the mechanisms underlying this phenomenon, resting metabolic rate was measured sequentially in six healthy obese women on a weight maintenance diet (more than 2,300 kilocalories), after 15 days of an 800 kilocalories carbohydrate-free diet, and after isocaloric sucrose replacement for an additional 15 days. The carbohydrate-free diet produced a 21 percent decline in resting metabolic rate (p <0.005) as well as a decrease in circulating triiodothyronine (41 percent, p <0.02) and insulin (38 percent, p <0.005) concentrations. Plasma norepinephrine levels also tended to decline (10 percent, 0.05> p <0.1). However, when sucrose was substituted, resting metabolic rate rose toward baseline values even though total caloric intake was unchanged and weight loss continued. The sucrose-induced rise in resting metabolic rate was accompanied by a rise in serum triiodothyronine values, but not plasma insulin or norepinephrine concentrations. Throughout, changes in resting metabolic rate correlated with changes in serum triiodothyronine levels (r = 0.701, p <0.01). In four obese women, a hypocaloric sucrose diet was given at the outset for 15 days. The fall in both resting metabolic rate and triiodothyronine concentration was markedly reduced as compared with values during the carbohydrate-free diet. It is concluded that carbohydrate restriction plays an important role in mediating the fall in resting metabolic rate during hypocaloric feeding. This effect may, at least in part, be related to changes in circulating triiodothyronine levels. Incorporation of carbohydrate in diet regimens may, therefore, minimize the thermic adaptation to weight loss.
Cliff, you have to distinguish between the effects of carbs on the one hand, and the differential effects of sugar v starch on the other.
As I've blogged (eg http://perfecthealthdiet.com/?p=4383), zero-carb diets invoke a glucose conservation program that downregulates T3 thyroid hormone level and metabolism. Restoring carbs in any form will restore T3 levels and metabolic rate. Starch works as well as sugar. That effect is all this study shows.
In this case "raising metabolism" was beneficial but not every dietary change that raises metabolism will be. Excess calories / overfeeding will raise the metabolism but is not a healthy practice over any extended period of time.
None of this supports a preference for fructose-bearing sugars over other types of carbohydrate.
hmmm...maybe so you can burn it off quicker to get it out of the body?
I think something's being lost in the big picture here. I'm not a sciencey type which puts me at a disadvantage in some ways, but it also gives me a more simplistic bigger picture view. I'm a fan of keeping things that are blatantly toxic out of the body, however, there are many things that fall into a gray are of being toxic at high doses- granted that doseage may be higher or lower for individuals. I put fructose in that category. From where I stand, the body can deal with it in small and even moderate amounts- particularly from fruit where it's usually attached to glucose. When we start talking about ingesting large amounts of juices from fruit- much more than we can find in nature- my first question is why? I'm not asking that rhetorically, I really want to know the benefit of doing so. I've heard the argument that it takes care of the morning cortisol spike. Why would I want to do that? I've heard that it replaces liver glycogen. Well so does excess glucose from starches after your muscles have been loaded up with glycogen. These arguments just aren't strong. Yes, I know that PUFA's compound the problem but I'd like to see at the least an epidemiological study of a group of people living on a high fructose diet and thriving. Outside of that, I would proceed with caution with the biohackers claiming that fructose in high doses is benign...
Edit: I also want to challenge the assumption that an elevated metabolism is always a good thing. From where I stand, metabolism is something that varies for a reason- it regulates the energy balance. Is there a reason I would want my truck idling at 2500rpm? I wouldn't want my body to either.
If I'm not mistaken, the activity of hepatic deiodinase (which converts T4 to T3) is downregulated when liver glycogen drops below a particular threshold. As such, carbohydrate restriction behaves in a very similar manner to a selenium deficiency, with the result being far less active thyroid hormone, even if T4 is at a normal level.
Simple. It triggers insulin after a certain level in the blood, beyond which it becomes toxic to nerves, eyes, etc. Insulin, in turn, triggers storage of nutrients to fat.
If sugar is so bad, why does it raise metabolism?
Because raising metabolism is bad? This seems to beg the question, not to mention take a grossly simplified approach that will likely confuse many people. There's so many other questions that could be asked to try and clarify the point that it would be easier if you could be mroe specific about the problem you're needing help with.
Sugar raises metabolism because it bypasses the most important control points in glycolysis (Glucokinsae and PFK-1. The product fructose turns into for glycolysis Fructose 1,6 bis phosphate stimulate the one remaining pathway). Whether the rise of metabolism is a good or a bad thing is dependent on many factors but most importnatly nutritional status. If people aren't nutritionally replete, they may not have the nutrients necessary for a high metabolism but the consumption of fructose will cause them not to be able to regulate energy production as tightly which will call for the use of precious nutrients.
the amount of sugar in just one can of coke is enough sugar to lower the metabolism of infection fighting blood cells by 75 percent. http://www.natural-pain-relief-guide.com/sugar-immune-system.html