In further analyses examining whether the source of proteins and fats favoured in low-carbohydrate diets - plant-based or animal-based - was associated with length of life, researchers found that replacing carbohydrates with protein and fat from animal sources was associated with a higher risk of mortality than moderate carbohydrate intake.
People who got 50-55 per cent of their calories from carbohydrates outlived those with very low-carb diets, on average, by four years, and those with high-carb diets by one year.
According to the BBC, researchers estimated that people in the moderate carb group were on average expected to live for another 33 years from the age of 50.
"We need to look really carefully at what are the healthy compounds in diets that provide protection", says Dr. Sara Seidelmann, Clinical and Research Fellow in Cardiovascular Medicine from Brigham and Women's Hospital, Boston, USA who led the research.
"While a randomised trial has not been performed to compare the longer term effects of different types of low carbohydrate diets, these data suggest that shifting towards a more plant-based consumption is likely to help attenuate major morbid disease".
Pasta is a high-carb dish. Their health was followed up for 25 years, allowing for factors that might alter the results, such as smoking, income and diabetes. Another important finding was that switching meat for plant-based protein led to healthier outcomes, in people with low-carb diets.
If you are going on a low-carbohydrate diet, better take it easy on the meat, too, experts advised Thursday.
However, it's not an excuse to pile your plate with them - as the study also found that eating too many carbs damages health. What's more, the study only assessed people's diets at two points in time, and it's possible that participants' diets may have changed during the 25-year study, which could have affected the results.
Because this was an observational study, it could not prove cause and effect.
Researchers noted that some of those animal products have been linked to the stimulation of oxidative stress, inflammatory pathways and biological aging - and could shorten lifespans.
The investigators also found that all low-carb diets may not be equal.
Co-author Walter Willett, a professor at the Harvard School of Public Health, said: 'These findings bring together several strands that have been controversial.
Professor Tom Sanders, of King's College London, added: 'The bottom line is that a balanced diet providing about half of the food energy from carbohydrates is best for health.' The study appears in the Lancet Public Health journal.
"Yet supporters of the cult of Low Carb High Fat (LCHF) eating, itself based on a lifestyle choice and the flimsiest of evidence supporting benefit, will no doubt disagree with this newest research on the subject".
If they instead started eating more plant-based food - such as vegetables, lentils, beans and nuts - the risk was lower. More research will likely follow but, in the meantime, it may be a good idea to stay away from low-carb diets. "If nothing else, this study provides some redress to this one-sided debate, and adds caution to such practice for long term management".
'Essential nutrients should be consumed above a minimal level to avoid deficiency and below a maximal level to avoid toxicity, ' he wrote. "This approach reduces our calories from fat to around a third of total calories, with protein making up around 20 per cent of the total, and alcohol calories sneaking in, too, where consumed".