Mr Prior used a combination of Facebook and YouTube entries to show the transformation that resulted in a 10.5 kilogram increase in his weight and a body fat increase from 9 to 16 per cent.

"I've just gotten back from the doctor where I had a complete physical. I'm 50 years old, I'm in good health ... I'm going to start drinking 10 Cokes a day ... that's the only change," Mr Prior said in the first of five video diaries.

"It's only 1400 more calories but we're going to see what the increased sugar and the increased insulin load, how that affects my health."

Mr Prior's reason for doing so was that, "according to the US department of Agriculture", more than 50 per cent of Americans consume the daily equivalent of 10 Cokes a day, although in the form of a combination of energy drinks, juices and other dietary forms.

Apart from the Cokes, his diet was unchanged; in fact he ate less because he lost his appetite.

By day nine, Mr Prior said he had gained eight pounds (3.6 kilograms) on his starting weight of 168 pounds (76.4 kilograms), having woken up at 176 pounds (80 kilograms).

He complained of stomach pains and not feeling well due to his change in diet.

"[I] don't feel good, I'm tired of drinking Coke. It's not the drinking it, it's the feeling full all the time, the not being hungry for other foods," Mr Prior said

A general follower of the Paleo diet, which incorporates a high amount of protein intake and low carbohydrate and sugar consumption, Mr Prior said he undertook the experiment to show that a high sugar intake, not a high fat intake, is a significant cause of weight gain.

"I'm Paleo, I eat a lot of fat, I eat a lot of protein and that's why I'm doing this because I want people to know that you gain weight not because of the fat you're eating ... the change is I'm eating sugar," Mr Prior said.

"It's sugar that makes you gain weight, it's grains, it's raised insulin level that makes you gain weight, not the fat."

Spokesperson for the Dietitians Association of Australia, Sonya Stanley, did not agree with the American's comments regarding insulin levels and said that consumption of excess kilojoules is what leads to weight gain and that levels can and do vary for different individuals.

"The [Australian] Dietary Guidelines include the recommendation to 'Limit intake of foods and drinks containing added sugars. In particular, limit sugar-sweetened drinks,' " Ms Stanley said.

"DAA encourages Australians to limit foods containing added sugar and little nutrition - such as sweetened carbonated drinks. Water is the best drink."

Coca-Cola South Pacific Pty Ltd public affairs manager Sarah Prestwood said all Coke products should be consumed in moderation and were clearly labelled with regard to their kilojoule content.

"It's no secret that the overconsumption of any food or beverage that contains kilojoules can lead to weight gain and this includes soft drinks," Ms Prestwood said.

"We always recommend our beverages be consumed in moderation as part of a healthy lifestyle that includes a sensible, balanced diet and regular physical activity."

Halfway though the challenge, the man said his measured body fat ratio had increased from 9 to 14 per cent and his weight was at 181 pounds (82.3 kilograms), up 13 pounds (5.9 kilograms) in just over two weeks.

At the 28-day mark the man reported a weight increase of 21 pounds (9.5 kilograms) at 189 pounds (85.9 kilograms). He said he was surprised at the amount of weight he had put on and blamed his raised insulin levels, which in turn caused his fat cells to store more fat.

At the completion of the 30 days there was a visible change in the man's appearance, illustrated in the before and after photos as well as his measured "Table of Physiological Change".

Mr Prior finished his final video by saying, "If I have to drink another Coke in a thousand years it will be one Coke too soon."