Like a growing number of experts, Dhurandhar believes the accumulation of excess fat is likely to have multiple causes beyond a potato-chip-and-couch-potato lifestyle.

Dhurandhar likens obesity to other chronic diseases. Just as the term cancer covers the numerous conditions that occur when abnormal cells divide out of control, obesity may not be a single disease but rather, a group of diseases tied together by the symptom of too much body fat, he said.

"It may look the same on the outside, but what triggers the condition varies from person to person and may require a different treatment to control," he said. "Down the road, we need to figure out why people become fat and then tailor their treatment to address the underlying causes."

Dhurandhar's own studies at Pennington Biomedical Research in Baton Rouge, La., focus on obesity-causing viruses. He discovered the viruses in chickens back in the 1980s and has since associated the presence of certain viral antibodies in the bloodstream of humans to increased body weight.

In one of his landmark studies of 500 people, 30 percent of the obese patients tested positive for the virus, compared to only 11 percent of the lean individuals.

Dhurandhar is quick to point out that he doesn't believe most obesity is infectious in nature, but said that the discovery of a "fat bug" should be a wakeup call to researchers, physicians and anyone struggling with their weight that there may be more to shedding surplus pounds than simply cutting back on calories and putting in a few extra treadmill sessions.

"What good does a starvation diet do if obesity is caused by a virus?" he asked.

Beyond viruses, scientists have identified at least 84 other potential contributors to obesity, Dhurandhar said. They range from genetic to biological to psychological to environmental. Currently, there are about a dozen of these obesogenic culprits under serious study in labs around the world, he noted.

For example, numerous studies now associate lack of sleep with an expanded waistline. Other studies have found that exposure to certain insecticides and plastics disrupt gut bacteria, which may stimulate appetite, slow digestion and accelerate fat storage. And some studies propose a link between the lifestyle habits of great grandparents and their great grandchildren's weight status.

"Not all the causes will wind up being treatable or preventable -- you can't do anything about what your great grandparents ate -- so we will have to focus our efforts on the ones we can control," Dhurandhar said.

Christopher Ochner, director of research development and administration at the Mt. Sinai School of Medicine in New York said he agreed with Dhurandhar's idea that there could be multiple contributors to obesity, but said it complicates matters to classify obesity as multiple diseases.

"At the end of the day, we still have the law of energy balance to contend with," he said. "If you ingest more than you expend you are going to gain weight, period."

Dhurandhar conceded that eating and exercise play a significant role in obesity, but said that role is not as well understood as the general public thinks.

"We've focused almost all our resources on the so-called 'Big Two' of diet and exercise for more than 50 years and it hasn't helped," he said. "We will have to move beyond 'eat less and move more' if we want to make progress."

Ochner said he agreed that trying to lose weight and keep it off in the long term by exercising and cutting back on calories has less than a 1 percent chance of succeeding. He acknowledged that the reasons for weight gain vary greatly for each individual and the precise formula for energy balance through diet and exercise is nearly impossible to determine.

"There is literally, there is no difference between an emaciated person starving to death and an obese person on a healthy weight loss diet in terms of physiological reactions," he said. "That is going to be a tough problem to solve."

So what do you think? Do you believe obesity comes down to personal responsibility or are there other factors at play that thwart weight loss efforts? Share your thoughts in the comments section below. Better yet, voice your opinion during today's obesity tweet chat at 1 p.m., ET.

Our ABC Health tweet chat is moderated by Dr. Richard Besser, ABC News' chief health and medical correspondent. The American Medical Association, The Obesity Society and the Robert Wood Johnson Foundation are among the health groups and distinguished experts joining the conversation on this important health topic. If you'd like to join in too,for more details.

(Reuters) - A skydiving instructor died and his student was seriously injured after crash landing in woods in southern Mississippi during a tandem jump, officials said on Sunday.

The instructor, James Horak Jr., 56, was among a group that jumped together after taking off from the Lumberton, Mississippi, airport Saturday morning, said Lamar County Sheriff Danny Rigel.

Other divers accompanying Horak told authorities that the cords Horak used to control the parachute appeared to be tangled, Rigel said.

"Something didn't look right on his main chute," Rigel said, adding the Federal Aviation Administration will investigate.

The name of Horak's student and the extent of his injuries were not immediately known, though he appeared to have suffered broken bones and a head injury, Rigel said.

Horak, of Pensacola, Florida, was an instructor at the Emerald Coast Skydiving Center in Elberta, Alabama. His biography on the company's website identified him as its most experienced instructor, with more than 4,000 jumps to his credit.

Phone messages left with the company Sunday evening were not immediately returned.

(Editing by Dina Kyriakidou, Jane Sutton, Doina Chiacu)

The 33-year-old first baseman suffered a partial tear in the foot last month and has been advised by the Angels medical staff that it would be better not to rush back.

"It was not an easy decision, as competitive of a player as I am," Pujols told reporters. "But I also understand wanting to look past this season."

Pujols has been dealing with nagging issues in the foot all season and has started 65 of his 99 games at designated hitter rather than his regular post of first base as a result.

A three-time National League MVP during his first 11 seasons with the St. Louis Cardinals, Pujols has not recaptured his stellar form since signing a lucrative deal to join Los Angeles prior to the 2012 campaign.

He batted .285 last year, previously the lowest mark of his career, and will end 2013 batting just .258. with 17 home runs and 64 RBIs. Pujols is eight homers shy of 500 and two RBIs short of 1,500 over his career.

The Angels sit near the bottom of the American League West and look likely to miss the playoffs for a fourth straight year. (Writing by Jahmal Corner in Los Angeles, editing by Nick Mulvenney)

Well, not just affordability, even if that is supposed to play a huge part. The ratings would reflect a school's "value" — which would factor in tuition, graduation rates, the percentage of lower-income students in attendance, average student loan debt, and earnings after graduation.

Over the last 30 years, tuition costs , leaving the average student with $26,000 in debt and making reform of the university system a necessity.

"Higher education cannot be a luxury," Obama told an enthusiastic crowd of students at the University at Buffalo. "It's an economic imperative."

Eventually, if approved by Congress, federal financial aid would be tied to those ratings, the idea being to coax universities into reducing the cost of an education. The president wants to put his system in place by the beginning of the 2015 school year.

Why it might workRight now, schools don't have much of an incentive to keep costs down, writes 's Matthew Yglesias:

Currently, federal student aid is distributed to colleges based on how many students they enroll. To get a bigger piece of the federal pie, schools like NYU just have to attract more students. They don't have to worry about the mountain of debt those students could leave with — in some cases, without even graduating.

Another factor that drives up costs? Colleges, much like hospitals, don't have to worry about losing "customers," writes Ezra Klein at :

Why it might not work"Defining the right quality metrics is difficult, and making sure you're not penalizing institutions that accept disadvantaged kids is crucial,"Klein. "And that's before you even get into the politics."

Yes, the politics. At first, the plan would seem to have bipartisan appeal. Obama is not suggesting an increase in spending on student aid; he is suggesting a change in how that money is spent.

Wasting less money on education "sounds pretty conservative," writescolumnist Jonathan Chait. "On the other hand, so did finding ways to get the government to spend less money on health care, a goal Republicans now deem a socialistic nightmare so terrifying they are mulling which catastrophic hostage threat they should use to destroy it."

Not only would Obama have to convince Congress to play ball, he would also have to contend with university administrators and alumni from some very powerful institutions. The University at Buffalo might be a good school and a great value, but it doesn't have as many influential, wealthy proponents as the Yales and Harvards of the world.

The battle over what "value" means will also be contentious. How do you rank earnings after graduation? Does that mean pumping out engineers will benefit your school more than producing liberal arts majors? Will schools turn away students they think won't graduate?

These are the questions Congress will have to answer, if lawmakers ever get around to taking up the issue.

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Over 420 drivers from all 50 states will compete in Salt Lake City for four days, challenging their driving skills, and knowledge of safety, equipment and the industry. From 18-wheeler five axle sleepers to tank trucks to twin trailersthey will drive a course that recreates situations truck drivers face daily. These maneuvers may include: an alley dock, a rear line stop, a side park, a scale stop, a right turn, a front line stop, and straight line driving through a diminishing clearance.

On August 24, one contestant will drive away as the Bendix National Truck Driving Championships Grand Champion.

"The Truck Driving Championships represent the culmination of the industry's dedication to safety," said Mississippi Trucking Association President David Roberts. "I congratulate all the contestants and I hope Mississippi cheers for our drivers this week."

ATA's National Truck Driving Championships and National Step Van Driving Championships include top professional truck drivers from around the United States competing at company, state and regional levels to make it to the national competition Aug. 21-24 in Salt Lake City. The NTDC annually attracts over 2,000 cheering friends, family, colleagues and spectators. For more information, visit the 2013 National Truck Driving Championships. Follow NTDC this week on.

is the largest national trade association for the trucking industry. Through a federation of 50 affiliated state trucking associations and industry-related conferences and councils, ATA is the voice of the industry America depends on most to move our nation's freight. Follow ATA onor on. Good stuff. Trucks Bring It!.

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LOS ANGELES (TheWrap.com) - "Inferno," the film adaptation of the new Dan Brown novel with Tom Hanks attached to star, will be released on December 18, 2015, Sony said Tuesday.

David Koepp is adapting the book from the author of "The Da Vinci Code" and "Angels & Demons," and was released in May.

Both novels feature the central character Prof. Robert Langdon, who was played by Hanks in the two earlier films, both of which were box-office hits.

In "Inferno," the villain threatens to unleash a plague and leaves clues from "The Inferno," Dante's 14th-century poem about hell.

NEW YORK (Reuters) - U.S. stocks fell slightly on Friday, and the Dow industrials posted the biggest weekly loss this year as rising bond yields hurt shares paying rich dividends and earnings from retailers disappointed investors.

The S&P 500 utilities sector, down 1.1 percent, led the day's decline as the yield on the benchmark 10-year U.S. Treasury note rose to a two-year high, making the highest dividend-paying stocks less attractive.

Nordstrom late Thursday was the most recent department store chain to miss revenue estimates. The upscale retailer cut its full-year sales and profit forecasts. Shares fell 4.9 percent to $56.43.

Earlier this week, Macy's reported an unexpected decline in sales and blamed hesitation by consumers. Macy's stock was down 2.8 percent to $44.99.

It was a second week of losses for the major indexes. The Dow fell 2.2 percent for the week, its biggest decline since June 2012, while the S&P 500 and Nasdaq registered their biggest weekly losses since June, 2013.

"Given how the consumer has been such a powerhouse, I think these are things that make you at least stop and wonder if you should be an aggressive buyer of retail stocks," said Eric Kuby, chief investment officer, North Star Investment Management Corp, Chicago.

The Dow Jones industrial average was down 30.72 points, or 0.20 percent, at 15,081.47. The Standard & Poor's 500 Index was down 5.49 points, or 0.33 percent, at 1,655.83. The Nasdaq Composite Index was down 3.34 points, or 0.09 percent, at 3,602.78.

For the week, the S&P 500 was down 2.1 percent and the Nasdaq was down 1.6 percent.

It was a third day of declines for the S&P 500, which also ended just below its 50-day moving average of 1,657, while the Dow ended below its 100-day moving average of 15,102. Breaks below these technical levels could add to selling pressure.

Adding to the market's concern, the Thomson Reuters/University of Michigan's preliminary reading on consumer sentiment in August slipped from July's six-year high.

Other data showed U.S. housing starts rose 5.9 percent in July, compared with a 9.9 percent drop in June. Homebuilders Pulte Group and Lennar Corp gained on the news.

Pulte shares rose 2.3 percent to $16.28, while Lennar advanced 1.8 percent to $33.88.

Green Mountain Coffee Roasters shares rose 3.3 percent to $76.38 after Nasdaq OMX said the company will replace Life Technologies in the Nasdaq 100 index on August 22.

Volume was roughly 4.8 billion shares traded on the New York Stock Exchange, the Nasdaq and the NYSE MKT, well below the average daily closing volume of about 6.4 billion this year.

Decliners beat advancers on the NYSE by nearly 2 to 1 while on the Nasdaq decliners beat advancers by about 13 to 11.

(Additional reporting by Havovi Cooper; Editing by Bernadette Baum, Kenneth Barry and Diane Craft)

SAN FRANCISCO (Reuters) - A bicyclist who fatally struck a pedestrian in San Francisco was sentenced to community service and probation on Thursday, after pleading guilty to felony vehicular manslaughter in what is believed to be the first such conviction in the United States.

After striking a plea deal to avoid jail time, Chris Bucchere, 37, was sentenced to 1,000 hours of community service and three years of probation for the death of 71-year-old Sutchi Hui last year, San Francisco District Attorney George Gascn said in a statement.

"Mr. Hui was a loving husband, father, and grandfather who tragically lost his life in an incident that could have easily been prevented," Gascn said. "Motorists, pedestrians, and bicyclists must share the road in a responsible way because there are dire consequences when traffic laws are disregarded."

Gascn has said the case marked the first felony vehicular manslaughter conviction in the United States against a bicyclist. His office last year prosecuted a similar case as a lesser charge.

Bucchere, a software developer, was riding his bicycle downhill in March 2012 when he entered a crowded intersection in the city's Castro District and collided with Hui, who had been crossing the street with his wife. Hui died of his injuries four days later.

Bucchere had been riding at about 30 miles per hour (48 km per hour) at the time, said Alex Bastian, a spokesman for the District Attorney's Office. Investigations into the collision showed that Bucchere used a GPS-based application that allows cyclists to compare speed records on a route and set personal records.

Witnesses of the crash told authorities Bucchere ran through a red light before slamming into Hui, and those witness accounts were a tie-breaking factor in the decision to prosecute the case as a felony, Gascn has said.

The plea deal was reached after Hui's son told prosecutors he did not want Bucchere to serve jail time for his father's death, Gascn said. A felony conviction for vehicular manslaughter could have carried a maximum sentence of six years in prison under California law.

Another bicyclist pleaded guilty in San Francisco to misdemeanor manslaughter last year. That cyclist received 500 hours of community service and three years of probation for striking a 67-year-old woman who later died.

A judge can decide in six months whether Bucchere's conviction can be reduced to a misdemeanor, Gascn said. A call and email for comment to Bucchere's attorney, Ted Cassman, were not returned.

(Editing by Cynthia Johnston and Lisa Shumaker)

The 76-year-old Czech-born Stoppard, who co-wrote the Oscar-winning screenplay for the 1998 film "Shakespeare in Love", came to fame in the theatre for writing plays such as "Rosencrantz and Guildenstern are Dead", "Jumpers" and "Arcadia".

"Harold was one of the reasons I wanted to write plays," Stoppard said in a statement from prize organizer English PEN, a worldwide writers' association and freedom of expression charity.

"His work dominated the foreground of my thoughts about theatre in the few years before I sat down to try to write a play in 1960."

The prize is awarded annually to a British writer or writer living in Britain, who, in the words of Pinter's speech on winning the Nobel literature prize, casts an "unflinching, unswerving" gaze upon the world.

"I had the sense not to attempt a 'Pinter play', but in other respects, as the years went by, he became and remained a model for the kind of fearless integrity which PEN exists to defend among writers, and most of us had occasion to feel humbled by his example," Stoppard said.

Stoppard will receive the award at a public event at the British Library on October 7, PEN said. He will share it with an "International Writer of Courage" chosen by him in association with English PEN's Writers at Risk Committee to recognize a person who has been intimidated for speaking out about their beliefs.

British poet Carol Ann Duffy shared last year's prize with exiled Syrian author Samar Yazbek, whose book "A Woman in the Crossfire" portrayed life inside the Syrian conflict.

(Reporting by Paul Casciato; Editing by Mark Trevelyan)

The 76-year-old Czech-born Stoppard, who co-wrote the Oscar-winning screenplay for the 1998 film "Shakespeare in Love", came to fame in the theatre for writing plays such as "Rosencrantz and Guildenstern are Dead", "Jumpers" and "Arcadia".

"Harold was one of the reasons I wanted to write plays," Stoppard said in a statement from prize organizer English PEN, a worldwide writers' association and freedom of expression charity.

"His work dominated the foreground of my thoughts about theatre in the few years before I sat down to try to write a play in 1960."

The prize is awarded annually to a British writer or writer living in Britain, who, in the words of Pinter's speech on winning the Nobel literature prize, casts an "unflinching, unswerving" gaze upon the world.

"I had the sense not to attempt a 'Pinter play', but in other respects, as the years went by, he became and remained a model for the kind of fearless integrity which PEN exists to defend among writers, and most of us had occasion to feel humbled by his example," Stoppard said.

Stoppard will receive the award at a public event at the British Library on October 7, PEN said. He will share it with an "International Writer of Courage" chosen by him in association with English PEN's Writers at Risk Committee to recognize a person who has been intimidated for speaking out about their beliefs.

British poet Carol Ann Duffy shared last year's prize with exiled Syrian author Samar Yazbek, whose book "A Woman in the Crossfire" portrayed life inside the Syrian conflict.

(Reporting by Paul Casciato; Editing by Mark Trevelyan)