But many people consuming a typical Western diet are exceeding such a limit by about 50 per cent, and may be putting themselves at an increased risk of certain cancers, said scientists from Washington University in St. Louis.
The research, published in the December issue of the American Journal of Clinical Nutrition, reports that people assigned to eat a long-term, low-protein, low-calorie diet had lower levels of hormone called insulin-like growth factor 1 (IGF-1), reported to be a promoter of cell proliferation and previously linked to pre-menopausal breast cancer, prostate cancer and certain types of colon cancer.
"Our findings show that in normal weight people IGF-1 levels are related to protein intake, independent of body weight and fat mass," said lead researcher Luigi Fontana from Washington University and the Istituto Superiore di Sanità in Rome.
"I believe our findings suggest that protein intake may be very important in regulating cancer risk."
Such preliminary research could muddy the waters yet further of the proposed benefits or risks associated with high-protein diets.
Low carbohydrate, high protein/fat diets have lost popularity amongst the public with critics saying that the approach puts followers at a higher risk of clogged arteries and heart attack in the long-term.
"We know that if we consume 50 percent more calories than recommended, we will become obese. But there is not a lot of research on whether chronic over-consumption of protein also has harmful effects," said lead researcher Luigi Fontana, from Washington University and the Istituto Superiore di Sanità in Rome.
Fontana's research, funded by the National Institutes of Health, involved three groups of 21 men and women, the first assigned to eat a low-protein, low-calorie, raw food vegetarian diet (average daily protein intake of 0.73 grams per kilogram of body weight), the second group was made up of endurance runners eating a standard Western diet (average daily protein intake of 1.6 g/kg body weight), and the third group was made up of sedentary people who also consumed a standard Western diet (average daily protein intake of 1.23 g/kg body weight).
Western diets are typically high in sugars, processed refined grains and animal products, said the researchers, and the recommended daily allowance (RDA) for protein is 0.8 g/kg body weight, equivalent to about 56 grams per day for a 70 kg man.
Fontana and colleagues report that blood levels of IGF-1 were significantly lower in the low-protein diet group than in either the equally lean runners or the sedentary people eating a standard Western diet.
"People on a low-protein, low-calorie diet had considerably lower levels of a particular plasma growth factor called IGF-1 than equally lean endurance runners," said Fontana in a release.
"That suggests to us that a diet lower in protein may have a greater protective effect against cancer than endurance exercise, independently of body fat mass."
The study is said to be a "hypothesis-generating paper" but more research is needed to clarify what that connection is.
"Eating too many calories increases our risk of developing obesity, diabetes, cardiovascular disease and of certain types of cancer related to obesity," said Fontana.
"We hope to further clarify what happens to cancer risk when we are chronically eating more protein than we need."
Earlier this year, British researchers from University College London reported "proof" behind why high protein diets enhance satiety and promote weight loss.
The UCL researchers reported that a hormone in the gut, peptide YY (PYY), increases on consumption of a high protein diet in normal and obese human subjects and produces a feeling of fullness (satiety).
But they were quick to distance themselves from the once-fashionable low-carb, high fat and protein diets, like the Atkins diet.
Source: American Journal of Clinical Nutrition December 2006, Volume 84, Pages 1456-1462 "Long-term low-protein, low-calorie diet and endurance exercise modulat metabolic factors associated with cancer risk" Authors: L. Fontana, S. Klein, J.O. Holloszy