My take on the recent ‘high protein diet as bad a smoking’ study

There are reports of a study doing the round in the UK press this week that warn us that eating a protein-rich diet is ‘as bad for us a smoking’. See here and here for examples of stories appearing in the ‘respected’ broadsheets the Telegraph and Guardian respectively. Reading the headlines of these pieces gives the distinct impression, I think, that low-carb and ‘paleo’ eating puts people on a fast-track to an early demise, particularly from cancer and diabetes. Given my nutritional stance (generally pro-low-carb and pro-paleo), perhaps not surprisingly, I’ve had quite a few emails asking for my opinion on this research.

The study concerned involved asking people to log what they ate over the course of a day, and then following them over a period of about 18 years. This type of research is ‘epidemiological’ in nature, which means it looks at associations between things. This study found an association between higher animal protein intakes and increased risk of death from diabetes, cancer and death overall in individuals aged 50-65. However, just because such a link was found, does not mean it’s protein that is causing the apparently harmful effects.

It might be, for example, that individuals who eat a lot of animal protein might also smoke more, and this is the real explanation for the link between animal protein and increased risk of death. Researchers can ‘control’ for these other factors (called ‘confounding factors’), and this was the case in this study. However, this process is far from perfect, and still leaves us with data that can only ever show associations (and not causality).

It is perhaps worth bearing in mind that this was a relatively small study. But would a larger study have been better? Or multiple studies showing the same thing? The reality is that epidemiological evidence is limited in its power by the very nature of this research, and having bigger or more studies does not magically transform a sow’s ear into a silk purse.

Imagine a study that finds a correlation between ice cream sales and shark attacks. One can imagine that more ice cream is sold when the weather is warm, and more people are likely to end up in the sea when the weather is warm too. However, the idea that ice cream actually causes shark attacks is probably incorrect, right? And it doesn’t matter if you have a mammoth study or 20 similar studies showing such an association, the fact is ice cream still doesn’t cause shark attacks.

This inherent weakness of epidemiological studies is the major reason why, these days, I hardly ever write about or comment on this sort of research. If it wasn’t for the fact that this recent study has had so much attention and me so many emails about it, I wouldn’t be writing about it at all.

The way the study has been reported, though, is not nearly as circumspect as it should have been, I think. We can lay the blame at the feet of the ‘science’ journalists who have reported this study in what might be termed a ‘sensationalist’ way. But, likening protein-rich diets to smoking appears to have come from one of the study authors: Dr Valter Longo is quoted in the Telegraph as saying:

We provide convincing evidence that a high-protein diet – particularly if the proteins are derived from animals – is nearly as bad a smoking for your health.

I have news for Dr Longo: No he hasn’t.

But there’s another part of this ‘research’ that appears to have been lost in translation. In individuals aged 66 or older, high protein diets were found to be associated with a lower risk of death overall, including a reduced risk of death from cancer. According to the authors of this study, it seems that somewhere around our mid-60s our protein needs flip from low to high. If this sounds faintly ridiculous to you, then that’s because it is (I think).

Crucially, when all individuals over the age of 50 were considered, no relationship was found between protein intakes and risk of death or risk of death from cancer. This, I would say, is the bottom line of this study, but it’s got completely buried in the ‘Atkins gives you cancer’ rhetoric.

Interestingly, this overall result was the first result to be reported by the authors in the study, and my suspicion is that their original intention was to perhaps find something meaningful here and leave it at that. However (and this is idle speculation on my part), it seems that after finding nothing, they decided to see what ‘meaningful’ results they could dredge from the data. In scientific parlance, this is referred to as ‘post-hoc analysis’. A colloquial way to describe it is ‘shifting the goalposts’.

The end result is that a weak study showing nothing much gets interpreted in a way that I believe is sensationalist, over-hyped and misleading. The problem here is that it might lead many to doubt the appropriateness of how they are eating and lead them to a diet that is altogether less healthy (such as one rammed full of carbohydrate).

Researchers and scientists have a responsibility to report their findings accurately and honestly. I’m not sure Dr Longo has done that here, at all. Likening protein-rich diets to smoking on the basis of epidemiological evidence is not only unscientific but potentially damaging. I wonder whether Dr Longo will reflect on his soundbite and wonder whether he might have (even unwittingly) put headlines in front of public health.


1. Levine ME, et al. 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. Cell Metabolism. 2014;19(3):407-417

57 Responses to My take on the recent ‘high protein diet as bad a smoking’ study

  1. john mason 6 March 2014 at 1:33 pm #

    As Zoe Harcombe points out “Dr Longo, has declared interests in (actually, he’s the founder of) L-Nutra – a company that makes ProLon™ – an entirely plant based meal replacement product.” Another case of ‘follow the money’

  2. paulc 6 March 2014 at 3:01 pm #

    erm, Dr. Briffa, you’ve missed out on the fact that what they are calling a high-protein diet isn’t really one. It’s just a typical western high-carb diet that just has a very slight amount more protein in it that what they’re calling a low-protein diet.

    It’s very disingenuous to call something high-protein when there’s 50% carbs in it…

    • Dana 8 March 2014 at 11:14 pm #

      That’s about what I thought. They never control for carb intake on studies like this.

      Something else they never seem to tease out is that because most people believe animal protein’s unhealthy, people who deliberately abstain from animal protein or deliberately eat less of it are also more likely to pursue behaviors considered healthy, such as taking up exercise or quitting smoking. Whereas a dedicated meat-eater, especially a dedicated red-meat-eater, is more likely to resent attempts at micromanaging what they eat and how or whether they pursue better health, and continue doing whatever they want without thought to the outcome.

      I’m also having a hell of a lot of trouble believing that they got ALL these study participants to fill out an ACCURATE questionnaire EVERY DAY from age 18 onward for years and years and years. Just not buying it.

      • Jean 9 March 2014 at 10:03 pm #

        I agree. This ridiculous pseudo science makes me angry especially because newspapers pay such attention to it. It is more likely that the group had more cancer and diabetes because they consumed more starch and sugar.

    • Dana 8 March 2014 at 11:14 pm #

      That’s about what I thought. They never control for carb intake on studies like this.

      Something else they never seem to tease out is that because most people believe animal protein’s unhealthy, people who deliberately abstain from animal protein or deliberately eat less of it are also more likely to pursue behaviors considered healthy, such as taking up exercise or quitting smoking. Whereas a dedicated meat-eater, especially a dedicated red-meat-eater, is more likely to resent attempts at micromanaging what they eat and how or whether they pursue better health, and continue doing whatever they want without thought to the outcome.

      I’m also having a hell of a lot of trouble believing that they got ALL these study participants to fill out an ACCURATE questionnaire EVERY DAY from age 18 onward for years and years and years. Just not buying it.

      • Richard David Feinman 9 March 2014 at 11:24 am #

        They did control for carbohydrate but I think that we make a mistake in trying to explain the results as if they were statistically sound and we need to see how they went wrong. I am not a statistician but statistics is not science. It is a series of methods which have to be applied appropriately. This study produces meaningless numbers. They don’t have to be explained. We need to bring out how the wrong analysis was done. Not easy especially when you have a hard-nosed, truculent character like Longo.

    • Gregory Barton 9 March 2014 at 12:43 am #

      … not to mention the margin of error inherent in people reporting what they ate for the last 18 years.

  3. Christoph Dollis 6 March 2014 at 3:42 pm #

    Does smoking decrease your risk of death as you get older?

    • William L. Wilson, M.D. 7 March 2014 at 3:09 pm #

      I tell my patients that when they reach 90 they can start smoking drinking to excess and having unprotected sex! Seriously, when you reach a certain age these lifestyle factors likely decrease in potency.

  4. Luigi 6 March 2014 at 5:50 pm #

    Maybe eating American grain fed beef and dairy does increase the risk. How much Omega 6 linoleic acid, an established risk factor, is consumed from both the meat itself and the oil used for cooking? This sort of “research” using whole “foods” originating from America is worthless. Do these journals never peer review research prior to publication?

  5. Eric 6 March 2014 at 6:03 pm #

    The most ridiculous part of this study, in my opinion, is that the data set was from a single 24-hour dietary recall survey and nurse-performed measurements for things like BMI, BP, etc. 18 years ago. To claim that this one day’s eating represents a lifetime eating habit beggars belief. They should have claimed “People who had that one heavy protein day 18 years ago got cancer at a higher rate…” It’s certainly more accurate.

  6. Vanessa Schaffeler 6 March 2014 at 6:57 pm #

    It was hardly a ‘high-protein’ diet – see this from the NHS link above:

    “n this study, on average people ate 51% of their calories in the form of carbohydrates, 33% as fat and 16% as protein (11% animal protein). This is likely to be higher in fat and lower in carbohydrates than that recommended on the “Eatwell Plate” which shows the relative proportions of food that we should aim to eat.”

  7. Chris 6 March 2014 at 8:30 pm #

    Yet, it’s so sad that a lot of people will take this message for granted.

  8. Sue churchyard 6 March 2014 at 8:58 pm #

    How cam a piece of cooked chicken possibly be as bad as a cigarette. The world has gone mad. X

  9. Lari Katz 6 March 2014 at 9:41 pm #

    I would expect a bias as the lead in the study, Dr. Valter Longo, has a vested interest in this company:

  10. Anne 7 March 2014 at 9:00 am #

    It says in the Guardian that “People who took part in the study consumed an average of 1,823 calories a day, with 51% coming from carbohydrates, 33% from fat, and 16% from protein, of which two thirds was animal protein.”

    So that’s high carb, not at all high protein !

  11. John B 7 March 2014 at 9:02 am #

    From observation: people everywhere are better nourished and healthier than ever before; in Western Countries people are living longer.

    Then main risk factor for disease is genetic; to lower risk people, should change their parents not diet or lifestyle.


    Anymore so than the endless ‘research’ and comical, hyperventilating media reports or willingness of politicians to believe whatever an ‘expert’ says no matter that ‘experts’ have been qrong every time whether about population explosion, new ice age/global warming or the economy?

  12. Clare 7 March 2014 at 9:19 am #

    I suspect that the benefits seen in the older members of the group, might be associated with a fundamentally simpler and healthier diets of previous generations.

  13. Pat Edwards 7 March 2014 at 9:23 am #

    I keep asking myself why the medical profession, ie those not affiliated to a commercial body, do not stand up to these people publicly and in the very press that publishes this rubbish? And then I realise that time is running out for free speech in the medical profession as soon they will all be working for the profit motive with little incentive for independent research at any level. You can’t be on your own here, John? I really fear for my grandchildren. They should be our incentive but I feel so powerless. We need a campaign to ensure that the press give proper opportunity for rebuttal to such bad science. I see that the NHS choices critique of Lango’s piece is highly critical but is this getting publicity? Time for another radio interview, John? Thank you for all your efforts.

    • Janet B 7 March 2014 at 4:13 pm #

      Well, it’s all down to the Emperor’s New Clothes, isn’t it. Nobody is going to ‘fess up’ any time soon about disgusting margarines awash with omega6 and other unwholesome poor quality foodstuffs we are constantly being told we must eat “for the good of our health” or for the overprescribing of statins, also ‘for the good of our health’. An awful lot of scientists, doctors, nutritionists – most of the medical profession probably, etc. would risk total loss of face.
      What could they say? “Sorry people, we think we ought to tell you that we made a bit of a mistake – we’ve made you fat and sick. Oops”

  14. John 7 March 2014 at 9:24 am #

    I am not that surprised at the association found. There is also a very strong association between dairy intake and certain types of common cancers (e.g. breast and prostate), so this fits. It may be that the growth factors and increased hormone production are to blame, with some carcinogenic compounds also in meats, particularly processed meats. As you get older these growth/hormone factors may become less important as your body may actually benefit, on balance, hence the associations found. Speculation I know, and proper research needs to be done on this (the dairy industry will not like that). The thing about epidemiological associations is that it helps to identify areas of potential causality that should be researched more thoroughly.

  15. Dr Mel 7 March 2014 at 9:38 am #

    Thanks John. I’m glad that the NHSChoices website has also given a balanced response. By the way, do you have a visual representation of the Eatwell Plate they refer to on NHS Choices? It would be useful to be able to share this with patients.

  16. Steve Cordingley 7 March 2014 at 9:41 am #

    Let’s not throw the baby out with the bathwater though… protein and IGF-1 is an issue. My personal needs for protein appear to be a bit higher than the 1g to 1Kg of lean bodyweight, but I do have to keep in mind that the more protein I take in, the more careful I have to be as ‘too much’ isn’t a good thing. Unfortunately, I haven’t been able to find anything that will reliably predict what is too much for my organism. I expect we’ll know when I die :-)

  17. Simon James 7 March 2014 at 9:59 am #

    I don’t know about anybody else, but if the single 24 hour dietary recall was taken following the first BBQ Saturday of the year, then my intake of chicken and beef would be considerably elevated. :-)

    Also, I lost interest in their findings when it became apparent that it was another one of those let’s-inject-mice-with-dodgy-compounds-to-prove-that-humans-will-get-a-nasty-disease experiments.

  18. Pete Grist 7 March 2014 at 11:16 am #

    Towards the end of a Guardian piece by Zoe Williams on the subject in G2 she writes the following:

    “But the overriding fact in all this is that this new study is wrong: the US data set from which it is drawn is fatally flawed and the link between protein and premature death is simply not demonstrable from this evidence. Jack Winkler, former professor of nutrition policy at Metropolitan University, explains: “They did a correlation between the national diet survey in the United States (NHANES), and some data on death by disease. They linked it up, then alleged that protein caused death. Now, NHANES suffers from what all diet surveys suffer, namely: you ask people what they eat and what you get back is lies. People respond normatively. They put themselves in the best possible light. They’re not harmful, deceitful lies. In the case of the British survey, people underreport how much they eat by 25% and adolescents by 30%. Underreporting they call it, but in plain English, it’s lies.”

    A study has just been published on what’s wrong with NHANES, which concludes: “Across the 39-year history of the NHANES, EI [Employment Insurance] data on the majority of respondents (67.3% of women and 58.7% of men) was not physiologically plausible.” In plain English, if they really ate what they said they’d eaten, they would no longer be alive. In two-thirds of cases.

    Winkler continues: “The practical consequence for the protein story is that you’ve got a correlation between food intake and disease, but the food intake data is so poor that any correlation is suspect. Academics sit in front of a computer screen and do data analysis. But they never question the quality of the primary data. I’m not being rude, but my attitude towards that study is contempt.”

    Pity it wasn’t given the same prominence in the main paper!

    • Steve Cordingley 7 March 2014 at 3:21 pm #

      So true – I read that article and had to read all the way to the end to see that. What came before though, was so tongue in cheek that I couldn’t tell if I was intended take this section of the article seriously or not.

  19. Jennifer Eloff 7 March 2014 at 11:20 am #

    Honestly, even on a low-carb diet, protein needs to be adequate and not excessive. A low-carb diet is a high-fat diet, with adequate protein, tons of veggies and some fruits. It is not a high-protein diet (you can read Protein Power by Dr. Michael Eades and he states how one get adequate amounts of protein, not excessive amounts). Since I do moderate low-carbing, anywhere from 50 grams to 150 grams in any given day, I don’t overdo protein in any case. On a very low-carb diet, people that eat huge amounts of protein, shoot themselves in the foot, as it turns into glucose in the body anyway, by a process called gluconeogenesis.

    • Jennie McGinlay 7 March 2014 at 6:02 pm #

      True – a low-carb diet doesn’t include excessive protein, but just what we need. I don’t really worry about how many grams I eat – I find it would be quite hard to overeat protein as there seems to be a natural limit to what I want.

  20. sula 7 March 2014 at 12:49 pm #

    Grass fed, organic meat and dairy, never hurt anyone. It is the quality of the protein that counts and most protein consumed by people today is dire, from sick, maltreated factory farmed animals, pumped full of antibiotics that never see the light of day. There is also an agenda here particularly for this Country, to destroy our farmers and farming.

  21. Arlene 7 March 2014 at 1:17 pm #

    They also seem to be lumping dairy in with this high protein diet. All high protein diets are not created equal,

    • paulc 8 March 2014 at 7:22 am #

      It’s not even a real high-protein diet. All three of their categories were really high-carb diets, just minor variations in the protein proportion.

      You’ll note that there was a “full court press” on this being high-protein by the media. Someone paid for that massive anti-high protein coverage…

      The processors are fighting back against low-carb high-fat by making false attacks on high-protein… by infering that Atkins and Paleo type diets are dangerous.

  22. Hilda Langham 7 March 2014 at 3:13 pm #

    Isn’t it a pity…….. the usual headline grabbing fiasco of the press!! Which unfortunately many will read and take as gospel. Thank heavens for steady, sound, provable advice such as Dr Briffa gives in both “Escape the Diet Trap” and “A Great Day at the Office”. People need to stop jumping on bandwagons and find out for themselves what works and what doesn’t. And what doesn’t work is swapping horses mid-race, fad diets and slimming clubs!!! Read these two books. Act on the advice (with support from your GP obviously if necessary before embarking) and look on it as a long-term health investment ……. not a short term fix.

  23. William L. Wilson, M.D. 7 March 2014 at 3:18 pm #

    I think Gary Taubes summed up this nutritional research quagmire in his recent article:

    Because of our lack of meaningful RCTs in nutrition, it’s more or less the Wild West out there when it comes to theories about how we should be eating. This paper clearly adds to the confusion.

    What’s even worse is we have a press that is clueless about the true nature of science.