The researchers conducted a 24-hour dietary recall (known to be highly inaccurate) and measured nutrient intake (protein, carbohydrates, fats, and calories) of 6,000 participants. These participants were categorised into three groups (low, medium and high protein intake) based on their consumption in one 24 hour period.
Eighteen years later they measured causes of death (cancer, diabetes, heart disease and all-cause mortality). The researchers theory was that protein increases IGF-1, which may increase the rate of growth in tumours already present in mice. In addition to this, 2,200 participants were tested for IGF-1 levels, although no information on how this testing was done was detailed in the study.
This was an observational study. This means they are looking for relationships between two or more phenomena and commenting on this association, however, this method of research cannot prove causation.
For example, you may look at the association between the increased presence of umbrellas in wet weather. Although umbrellas are often present when it rains, it doesn’t prove that they cause it to rain!
Unfortunately, claiming causation based off of an association is exactly what these researchers have done. Hence the sensationalism of the headlines.
Overall, our human and animal studies indicate that a low protein diet during middle age is likely to be beneficial for the prevention of cancer, overall mortality, and possibly diabetes through a process that may involve, at least in part, regulation of circulating IGF-1. Having said this, is it the low-protein component or is it due to the possibility that those who consume ‘high’ protein generally lead a relatively unhealthy lifestyle. After all, protein can be a Big Mac or a piece of steamed fish. Big difference.
In short, there are many influencing factors that have been ignored in this study. For example, those who eat more meat are typically not living healthy lifestyles. They may be inactive, consume less fruits/vegetables, smoke, consume high amounts of added sugar, alcohol, chemicals and preservatives, etc. They likely live the typical Western life. Despite the ability to control statistically for these factors in an equation, you cannot control physiologically for the interactions, and you certainly cannot pick one factor out of the myriad and claim it is the main cause.
Findings of many studies to date also indicate that it may be important to avoid low protein intake and gradually adopt a moderate to high protein to allow the maintenance of a healthy weight and protection from frailty.
In addition, the authors claim a benefit of increasing the consumption of plant proteins, however, the results from the mice studies where animal protein was actually replaced with plant proteins do not support these statements. There was no effect on tumor growth regardless of type of protein consumed. Not to mention the fact that mice, unlike humans, do not consume very much of their natural diet from protein sources (primarily herbivores).
Despite the very similar rate of cancer death per group, the authors described this as a 70% increase in cancer mortality with higher protein consumption, triggering a media sensation, despite the absence of these statistics (it seems they have calculated this figure over the entire cohort, rather than the categorised groups).
Next the authors claim that protein consumption increases the release of insulin and IGF-1, which increases the growth of existing cancer cells.
It does not cause the development of cancer. If IGF-1 and insulin caused the development of cancer then we should all avoid exercising (as it’s a powerful stimulator of IGF-1) and eating as every time we eat (especially carbohydrates) insulin is released to maintain normal blood glucose levels.
It’s also worth noting that the author (who supervised this study) is Victor D. Longo (VDL), the founder of the company, VDL. VDL, designed the study and obtained funding from the Nation Institutes of Health (NIH). The NIH had no role in study design, data collection and analysis, or the writing or and publishing of the manuscript. VDL has an equity interest in L-Nutra, a company that develops medical food. L-Nutra’s products are a “formulation of natural nutrients with the ability to provide nourishment and allow subjects to enjoy a combination of good and mostly organically grown and plant-based food.”
In summary, there appears to be a vested interest from the author of this study and some exaggerated and unfounded claims, which have eventuated in a sensational media storm. I know we all aim to do the best we can for our health and sensational claims, such as this, don’t make our decisions any easier. I felt compelled to write this blog to clarify a few things.
At the end of the day, a balanced diet containing lean protein (beef, fish, chicken, dairy, eggs) and loads of colourful, fresh plant foods will cover all bases. I don’t advocate “high” or “low” anything as “high” is more than your body can use, which is useless and “low” is less than your body needs, which is also useless. Adequate amounts of lean protein, unprocessed carbs and essential unrefined oils is the best ratio for optimum health and longevity.
As I always say – you can’t believe everything you read!