Is excess protein as bad for you as smoking?

I was getting ready for work the other morning when the other half ran in looking a tad panicked. He's a big gym goer, and therefore a big protein fan, and had just read the headlines that PROTEIN CAUSES CANCER.

Sounds like something the daily mail would say doesn't it? 'Cept this time the claim was from some fancy scientists, published in a fancy journal. The newspapers were going mad with the idea that steak and salad was as detrimental to your health as smoking some cigarettes. Really Science Daily? 

First off, I'd say those sort of suggestions are a bit irresponsible no? We know there's a link between cigarettes and cancer. Black and white, do one and you massively increase the risk of getting the other. It's taken a lot of hard work to get that fact out across the world, and I don't think the guys that published this paper meant that at all. It lead to the NHS releasing this. 

The paper everyone is talking about came from Professor Valter Longo's laboratory, at the University of Southern California, and was published in Cell Metabolism. This means it's not open access (BOOOO!) and therefore isn't available for everyone to read, but I'll let you keep Game of Thrones for your bedtime reading and do the hard work for you. 

To start with, the title sounds a little different to "Excess protein causes as much cancer as smoking"...

Low Protein Intake Is Associated with a Major Reduction in IGF-1, Cancer, and Overall Mortality in the 65 and Younger but Not Older Population

Basically: lower protein in your diet reduces your risk of cancer if you're younger than 65.

It's a really interesting paper and has got some great data in it. It suggests possible links between high animal protein intake and cancer prevalence in the 50-65 age group (which is pretty narrow).

The trial was carried out on about 6000 American adults aged 50 and upwards, with a follow-up period of 18 years. They also tested some of their findings from the study population on mice and in cells. 

For the 50-65 year old age group, consuming high levels of animal protein (considered to be 20% or more of their diet) resulted in a 4-fold risk of dying of cancer. But, in the over 65s category, higher protein levels were associated with the opposite: a 60% reduction in the number of cancer deaths when compared to the low protein (10% or less) group. 

From this, they suggest that a reduced protein diet, followed by an increase in protein consumption once you're eligible for a bus pass might be a good way to go. But there need to be more studies. 

They also monitored levels of IGF-1 in their participants and found that high levels of the growth factor were found in high-protein consuming groups, and this was then related to the high cancer prevalence. I.e. Lots of protein = more IGF-1 in our system = higher risk of cancer. 

After this, they presented data looking at the effect of protein consumption on tumour growth. Mice on high and low protein diets were injected with cancer cells, and the rate of tumour growth was monitored. They found that while all mice on high protein diets had developed tumours, this dropped by 10-20% in mice in low protein diets. This suggests that high protein levels help to promote tumour growth. Coming back to the IGF-1 stuff from earlier, they also found that the mice on a low protein diet had significantly lower levels of IGF-1 in their system. Again, less protein = less IGF-1 = lower risk of cancer. 

In mice. In one study. While the data is very interesting and compelling, I would say there's no need to throw those special offer steaks out of the freezer. Unless they've been in there a while... 

It could suggest that a low protein diet could help during cancer treatment. This isn't the first time protein and cancer have been mentioned together: high amounts of meat or animal fats in our diet have also been linked to breast (open access paper analysing current studies) and colon cancer (open access paper).  

It appears to be limited to animal protein though, vegetable protein is fine. 

I'm inclined to stick to the "everything in moderation" mentality. On that note...cake anyone?