A low protein diet increases snacking
A study published in PLoS One that shows that having a lower percentage of protein in the diet can lead to more snacking behaviour and more perceived hunger.
The team from the University of Sydney, led by Alison Gosby, wanted to test whether something known as the protein leverage hypothesis, or PLH, which suggests that a biological preference for a high protein diet, combined with a decrease in the proportion of protein in the diet in relation to fat and carbohydrate, can lead to obesity, applies to humans, as it does in other species.
Obesity is a huge problem (no pun intended) - almost a quarter of British adults are now classed as obese. Previous work in the United States has shown that over the last 30-40 years, protein intake has decreased from around 14% of the diet to 12.5% of the diet, and total energy intake has increased. The possible reason for this is that due to a lower intake of protein at mealtimes, people are craving extra protein and seek it from snack foods, which then increase their total daily energy intake.
In this study, participants were fed either a 10% protein, 15% protein or 25% protein diet for three four day periods. Their total energy intake and their perceived hunger levels were monitored over each four day period. Their main meals were regulated to contain the right amount of protein, but also available were 'anytime foods' like cheese scones, yoghurt or muffins.
They found that the participants on the 10% protein diet increased their total energy intake by 12% compared to those on the 15% protein diet. And it was the 'anytime' snack foods that made up 70% of the increased energy intake, rather than just eating more of their provided meal at mealtimes. It also tended to be the savoury snacks that the participants preferred, which the researchers suggest is due to the association of protein with savoury food rather than sweet. There wasn't any significant difference in energy intake between the 15% and 25% protein diets, suggesting that increasing protein in the diet above a certain amount will not necessarily decrease intake of other foods.
Average perceived hunger levels across the day didn't differ between the diets, but on the 4th day, participants on the 10% protein diet reported significantly more hunger 1-2 hours after breakfast than those on the 25% protein diet.
So what do these results mean in the context of the protein leverage hypothesis? Well, the researchers are keen to point out that this is only a small study, and alone it doesn't prove that the PLH is responsible for the increased levels of obesity in society, but they point out that along with other larger studies and the fact that protein intake has indeed decreased over the last 30-40 years, coinciding with the rise in obesity, it does seem to support the hypothesis.
They also mention that if the participants on the 10% protein diet continued to maintain their increased energy intake that they showed over the 4 day trial, without increasing their activity level, they could expect to put on a kilo every month!