Consumption of Green Tea May Help Prevent Obesity

Grove KA, Lambert JD. Laboratory, epidemiological, and human intervention studies show that tea (Camellia sinensis) may be useful in the prevention of obesity. J Nutr. 2010;140: 446-453.

Green tea (Camellia sinensis), a popular beverage worldwide, contains large amounts of polyphenols known as catechins: (-)-epicatechin, (-)-epigallocatechin, (-)-epicatechin-3-gallate (ECG), and (-)-epigallocatechin-3-gallate (EGCG). A cup of brewed green tea contains 240-320 mg of catechins, with EGCG accounting for 30% to 50% of that amount. Green tea also contains the xanthines: caffeine, theophylline, and theobromine. It has been studied for its potential health benefits and its effects on certain chronic diseases. Obesity, which affects about 20% of U.S. adults, is a risk factor for chronic diseases (e.g., diabetes, cardiovascular diseases, and cancer). These authors summarize the literature on the potential efficacy of tea to prevent obesity.

In their review of laboratory studies, the authors focus on mechanistic data from animal model studies that have examined the effects of tea on obesity and related pathologies, including diabetes, hypercholesterolemia, and fatty liver disease. Most studies have used green tea, green tea extract (GTE), or pure EGCG in both genetic and dietary models of obesity.

One cited study reported that treatment with 7.0 µmol/g dietary EGCG for 15 weeks reduced body weight gain in male mice fed a high-fat diet compared with control mice. The treated mice had significantly lower adipose tissue weight, fasting blood glucose, fasting plasma cholesterol, and plasma alanine aminotransferase levels. The same investigators reported that short-term dietary EGCG treatment of obese mice tended to reduce body weight gain compared with high-fat-fed controls. “This treatment regimen represents a more realistic obesity-related application of EGCG or green tea supplementation, because the most likely consumers of these products would have a preexisting weight problem,” state the authors. Other cited studies, as well as one including rats fed a normal-fat diet, support these findings.

Regarding tea and genetic animal models of obesity, the authors cite a study of the efficacy of GTE in obese, leptin-deficient mice, in which there was no significant effect on body weight. The study did, however, report higher plasma high-density lipoprotein cholesterol and lower hepatic triglyceride levels in the GTE-treated mice.

Few studies have examined the interaction between tea polyphenols and exercise; however, the animal studies cited by these authors support the benefits of tea polyphenols plus exercise in reducing body weight gain.

According to the authors, the “in vivo effects of EGCG may be explained by underlying mechanisms suggested by in vitro studies of de novo lipogenesis, lipid absorption, and carbohydrate absorption and utilization.” Several studies have begun to examine the effects of tea polyphenols on fatty acid synthase. Two studies have reported that EGCG can inhibit pancreatic lipase activity, but the effective concentrations in these studies varied.

The authors cite several studies in dietary models of obesity that have examined the role of green tea-mediated modulation of glucose uptake and disposition in obesity prevention. The findings from two studies indicate that treatment with green tea can increase carbohydrate catabolism. In vitro studies have suggested that EGCG and ECG play a role in inhibiting glucose uptake in the gut.

Most studies of animal models of obesity and tea have found no significant effect of tea or tea components on energy intake. The exceptions are two studies cited by these authors: one reported a significant decrease in food intake by mice treated with Oolong tea extract compared with untreated mice, and the other study reported that 0.5% tea catechins reduced energy intake by 5.6% (the trend was not significant, however).

Regarding human studies, the authors note that there are few epidemiological studies examining the impact of tea on body weight and other obesity-related markers. More interventional studies have been conducted. In one study of healthy Japanese men, the participants consuming high-catechin tea for 12 weeks had lower body weight, waist circumference, and body fat mass compared with baseline values. In a follow-up study by the same investigators, 240 obese subjects were treated with a catechin-enriched green tea beverage or a control green tea beverage for 12 weeks. Those in the high-catechin beverage group had a significant decrease in body weight, total fat area, and visceral fat compared with baseline values. These decreases were greater than those in the low-catechin control group. The authors note that the results of studies on tea and body weight and body fat have not been “universally positive,” citing some studies that reported no significant effects of green tea consumption on body weight.

The authors further cite a study that reported a beneficial effect on weight loss and weight maintenance following weight loss with green tea consumption and a study that showed a trend toward a greater decrease in body weight with green tea and exercise, compared with exercise only. “Further studies on the interaction between tea and exercise in humans are warranted,” say the authors.

U.S. sales of green tea-based dietary supplements are increasing, partly because of the number of reports describing the potential antiobesity and other beneficial effects of tea and tea polyphenols. Green tea-based dietary supplements can potentially deliver a much higher dose of catechins than do green tea beverages. Since 1999, say the authors, 34 case studies have linked the consumption of green tea-based supplements to hepatotoxicity. Laboratory studies in animals have generally supported the supplements’ potential toxicity at high doses. “These findings suggest that caution should be exercised in the use of green tea-based dietary supplements and that further studies are needed to determine the upper limit of safety for bolus dosing with tea polyphenols as well as the underlying mechanisms of toxicity.”

The authors conclude that “laboratory studies in animals, a limited number of epidemiological studies, and small-scale human intervention studies support the hypothesis that tea and tea polyphenols have beneficial effects on weight gain, weight loss, and prevention of obesity.”

—Shari Henson

DNA robots get sophisticated by Jef Akst

Scientists are one step closer to creating molecular robots that may eventually perform complex tasks, such as building nanomolecules or delivering drugs to target tissues.

They have constructed DNA-based robots that can walk along a specific path unaided or collect various nanoparticles along an assembly line, according to two studies published this week in Nature.

“This has the feel to me of the beginning of a technology revolution,” said Andrew Ellington, an evolutionary engineer at the University of Texas at Austin and the vice president of the International Society for Nanoscale Science, Computation and Engineering, who was not involved in the research. “This work will absolutely pave the way for how you build molecular robots.”

The robots built in one study are a type of DNA walker, called a molecular “spider.” They are minute, mobile molecules that move along a flat surface made out of folded DNA, known as DNA origami, binding to and unbinding from the surface as they go.

The movement of these spiders is largely random, however, said biochemist and study co-author Milan Stojanovic of Columbia University. But together with several other big players in the nanotechnology and DNA computing fields, including Nils Walter of the University of Michigan, Erik Winfree of the California Institute of Technology, and Hao Yan of Arizona State University, Stojanovic designed a DNA origami surface that directed the DNA spider down a specified path (see video).

“You just have to start it, and it walks the path,” said chemist Kurt Gothelf, director of Centre for DNA Nanotechnology at Aarhus University in Denmark, who was not involved in the research.

The spider is fueled by the chemical interactions its single-stranded DNA “legs” have with the origami surface. In order to take a “step,” the legs first cleave a DNA strand on the surface, weakening its interaction with that part of the origami surface. This encourages the spider to move forward, pulled towards the intact surface, where its interactions are stronger. When the spider binds to a part of the surface that it is unable to cleave, it stops.

In essence, the researchers created a DNA spider that can “sense the environment,” Stojanovic said — “molecules that respond [to environmental] cues and behave [in] certain programmable ways on their own.” The next step, he added, is to increase the complexity of movements performed by such autonomous robots by compiling “a collection of rules [of] interactions between molecules and between molecules and environment.”

A fluorescence video microscopy-generated animation of a DNA spider moving along the designated path from the green-labeled start site towards the red-labeled goal. Each colored dot represents its position at a given time over the 40-minute observation period (see legend).

Credit: Nils Walter, Anthony Manzo, Nicole Michelotti and Alexander Johnson-Buck, University of Michigan

Meanwhile, Nadrian Seeman of New York University and his colleagues have designed another type of DNA walker that can collect nano-sized “cargo” as it moves. Unlike the autonomous spider, the cargo-collecting walker is controlled by single strands of DNA added by the researchers to direct the robot. These strands instruct the robot to move past an “assembly line” of three small loading devices, also made out of DNA, each containing a gold nanoparticle. Each loading device can be programmed to either donate its cargo to the passing walker, or keep it, such that the walker can receive anywhere from zero to three particles along its short (less than 200 nanometers) journey.

It’s “like an automobile assembly line,” Seeman said. “We have the option to either add or not add various components to [the walker] depending on how the devices are programmed.”

One possibility for future experiments will be to combine the advances of each of the two papers into one complex, autonomous DNA robot, said Lloyd Smith of the University of Wisconsin, who wrote an accompanying review in Nature. “It’s going to take more work to take it to that next level, [but] bringing those two things together is going to be the next step towards” a fully autonomous, functional nano-sized robot.

Another future direction, the researchers agree, would be to scale up the length of the pathways and the complexity of the behaviors. But even once greater levels of complexity are achieved, what can actually be done with the little robots is still up for debate. “This whole field,” which is still in its early stages, Smith said, “hasn’t really found the application yet.” DNA robots have thus far proven to be capable of fairly sophisticated manipulation at the nanoscale, but the practical uses of this novel technology are still a little unclear.

One popular idea is to use cargo-collecting robots to construct nanomolecules that would be difficult to make using traditional methods, because of the control they offer researchers at such a tiny scale. “The ability to hold a molecule in a particular position and hold another molecule in a defined position could open up possibilities in organic synthesis,” said Smith. Another possibility is their use in drug delivery, said biochemist William Shih of Harvard University, who did not participate in the studies. “Having a very smart robotic delivery system could do a lot better job of killing the disease tissue and do far less damage to our otherwise healthy tissue,” he explained.

But most agree that these potential applications are yet to be realized; the current work merely shows “proof of principle” that such complex behavior might one day be achieved using this technology, Seeman said.

“I think these are both really, really significant papers, not because of what we can do with [these robots] now, but because of what we can do with them in the future,” said Ellington. They are “paving the way to a future where we can do practical DNA technology.”

H. Gu, et al., “A proximity-based programmable DNA nanoscale assembly line,” Nature, 465:202-5, 2010.

K. Lund, et al., “Molecular robots guided by prescriptive landscapes,” Nature, 465:206-10, 2010

Read more: DNA robots get sophisticated – The Scientist – Magazine of the Life Sciences http://www.the-scientist.com/blog/display/57400/#ixzz0oz3tm7it

Supplements Better Than Nothing By Sheah Rarback

srarback@hotmail.com

It would be a healthier world if everyone enjoyed fruits and vegetables, but unfortunately, that is not the case. Most Americans are not eating the recommended minimum of five servings a day, and for kids the most commonly consumed “vegetable” continues to be potatoes — as in French fried.

At least once a month someone sits down with me and starts our counseling conversation with, “I don’t like vegetables and I don’t want to be told to eat them.” It is challenging. Research demonstrates a reduced risk of chronic disease with a plentiful intake of produce, so sometimes an alternative is required for the vegetable-resistant.

One option is a powdered fruit and vegetable supplement. These supplements are made by juicing and then drying fruits and veggies at low temperatures, removing water, sugar and fiber.

The companies that produce the supplements fund academic research that is published in peer-reviewed journals. The most recent was in the April 2010 online edition of Molecular Nutrition and Food Research. This double-blind study of 117 healthy men and women measured changes in inflammatory blood markers after subjects consumed either placebo or two different powdered fruit and vegetable supplements. The goal is to have low levels of inflammatory markers, since inflammation increases risk for heart disease, diabetes and cancer.

After 60 days, the subjects receiving the fruit and vegetable supplements had lower levels of inflammatory markers, as well as higher blood levels of antioxidant vitamins, when compared to the group receiving placebo.

These findings are consistent with most previous research. Similar findings have been reported for people eating fruit and vegetables or enjoying a Mediterranean vegetable soup. These results show changes in blood levels — though not less disease — in people taking supplements. Long-term studies are needed to demonstrate disease changes.

For optimal nutrition, food is always the first choice.

Any whole food pill or powdered drink is meant to be a supplement to a varied food intake. But it’s good to know there are tested alternatives available if you are not getting your five servings a day.

Sheah Rarback is a registered dietitian and on the faculty of the University of Miami Leonard M. Miller School of Medicine. Her column runs every other week.

Read more: http://www.miamiherald.com/2010/05/18/1634231/supplements-better-than-nothing.html#ixzz0oZ02TFHA