Just in case you were avoiding all carbs like the plague, new research has suggested that a high carb, low protein diet is the most effective for stimulating a hormone with life-extending and obesity-fighting benefits.
The hormone in question is Fibroblast Growth Factor 21 -- also known as FGF21 if you're feeling particularly sciencey -- which has been touted as the "fountain of youth" hormone.
To get the lowdown on carbs, The Huffington Post Australia spoke to lead author of the new study out of University of Sydney's Charles Perkins Centre, Dr Samantha Solon-Biet.
The study was conducted in collaboration with the ANZAC Research Institute, Macquarie University, EWOS Innovation in Norway and the Pennington Biomedical Research Centre in Louisiana, U.S.
"Our group has actually published a large body showing that diets that are low in protein and high in carbohydrates have a lot of beneficial effects for mid- to late-life health in mice," Solon-Biet told HuffPost Australia.
"There's been a lot of interest in this hormone called Fibroblast Growth Factor 21, and we know this can be influenced by diet. In fact, the hormone is now being called a miracle hormone or a 'fountain of youth' hormone.
"The reason why FGF21 is so interesting is because high levels of this hormone has been shown to play a huge role in driving things like appetite, improving metabolic health and immunity, and can even extend lifespan in mice."
If you're thinking 'yeah, in mice, not people', Solon-Biet also said the same results have been found in humans.
"It's really important to say that this year we also published work looking at FGF21 levels in humans, and we found that, again, a low-protein and high-carbohydrate diet rapidly increases FGF21 in the same way that it does in mice. Our findings are really possible to be translatable to humans," Solon-Biet said.
This particular diet has also been associated with improved markers of health -- for example, improved blood pressure, insulin levels, glucose levels, blood lipid levels and all these beneficial effects.
One of the most interesting parts about FGF21 is that the hormone can be elevated in "really conflicting conditions".
"For example, it can be elevated in starvation and obesity, or in high intake or low intake of food, or even in both insulin resistance and insulin sensitivity," Solon-Biet explained.
"Using nutritional framework, our team was able to help reconcile these findings and we did this by carrying out a really large mice study. We published most of this in 2014 but we took a second look at all the data and looked at how macronutrients (proteins, carbohydrates and fats), as well as energy, interact together to influence levels of FGF21."
What Solon-Biet and her team's research showed was that a diet low in protein and high in carbohydrates was the most effective way to increase the levels of this hormone.
"This particular diet has also been associated with improved markers of health -- for example, improved blood pressure, insulin levels, glucose levels, blood lipid levels and all these beneficial effects," Solon-Biet said.
"It makes it a very interesting hormone and, in fact, it's now being investigated as a therapeutic target for the treatment of cardiovascular disease and diabetes."
Now, you may be wondering what this ratio of carbs to protein is. Well, it's higher than you thought.
"We found that the optimum combination of protein and carbohydrates was one protein for 10 carbohydrates. So, a one in 10 ratio," Solon-Biet told HuffPost Australia.
"This is interesting because it seems to coincide beautifully with the diet of the Okinawan people of Japan, who are actually the longest lived population in the world. It's called the Okinawan diet."
Naturally the Okinawan people eat a low protein, high carbohydrate diet. If you're having a 'hallelujah' moment and are about to inhale all the cakes and doughnuts you possibly can, hold up.
"It's mainly lean meats and fish, and their carbohydrates are more of the complex, slowly digested carbohydrates, so your vegetables and high fibre foods. Not our current carbohydrates which are so easily accessible -- chips, doughnuts, pizza and pasta.
"So there's a clear distinction to be made that a low-protein, high-carbohydrate diet doesn't mean you can eat all the cake in the world."
In regards to the third macronutrient, fat, Solon-Biet said it doesn't have as much of an effect on FGF21 levels as carbohydrates.
"Fat didn't appear to have, in our mice at least, a major effect on driving FGF21 levels," she said.
"There is literature out there saying that a ketogenic diet increases it (a ketogenic diet means a high fat diet). However, when we look at it further, the reason why it increases, we think, is because it's a high-fat and low-protein diet, and that the low protein is the key to the elevation of FGF21."
If you're about to tell all your Paleo friends to suck it, don't be too hasty.
"I think there is something to be said for the high-protein diet in that it does help you lose weight. In fact, we've shown that in our mice," Solon-Biet explained.
"Mice that are on a very high-protein diet are much leaner. They have a lot less body fat and they have more muscle mass, but in the long run they have worse health and a shorter life."
However, that doesn't mean you have to choose between a super ripped body or eating lots of carbs (and possibly reduce your risk of lifestyle diseases and lengthen your life). You can do both.
"Exactly. It doesn't mean we have to stick with the same nutrient combination or diet throughout life. We can change it as we go, I think," Solon-Biet said.
"I have no definitive evidence to say that, but I think eating a high protein diet when you're younger, and switching over to a lower protein diet could actually be beneficial to you."
The take home message from all of this? Carbs are not bad for you.
"Yes that is a very good way to say it. Carbs are not the enemy," Solon-Biet said.
"I'm not a dietitian but I think it's really safe to say that if we were to generalise these findings into humans, I would say moderate amounts of lean protein in the diet, and high in complex, slowly digested carbohydrate to promote gut health would be the way to go."