High protein diet not as bad for you as smoking

Behind the Headlines

Wednesday March 5 2014

High protein diet plans, such as the Atkins, have become popular is recent years

Smoked bacon: probably not as bad for you as smoking cigarettes

“People who eat diets rich in animal protein carry similar cancer risk to those who smoke 20 cigarettes each day,” reports The Daily Telegraph.

We have decades of very good evidence that smoking kills and – fortunately for meat lovers – this latest unhelpful comparison with high protein diets largely appears to be a triumph of PR spin.

The warning was raised in a press release about a large study which found that for people aged 50-65, eating a lot of protein was associated with an increased risk of dying.

However, the study, which assessed the diets of Americans in a single 24-hour period (rather than long-term), found in those aged over 65 that a high protein diet was actually associated with a reduced risk of death from any cause or from cancer. These differing findings meant that overall there was no increase in risk of death, or from dying of cancer with a high protein diet.

How much protein should I eat?

In 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.

There are several reasons to be cautious when interpreting the results of this study, including that the researchers did not take into account important factors such as physical activity in their study.

The claim in much of the media, that a high protein diet in middle-aged people is “as dangerous as smoking” is unsupported.

We need to eat protein, we do not need to smoke.


Where did the story come from?

The study was carried out by researchers from the University of Southern California (USC) and other research centres in the US and Italy. It was funded by US National Institutes of Health, National Institute on Aging, and the USC Norris Cancer Center. The study was published in the peer-reviewed journal Cell Metabolism and has been made available on an open access basis to read for free.

In general, reporting of the results of the study was reasonable. However, the prominence given to the story (which featured as a front page lead in The Daily Telegraph and The Guardian) in the UK media seems disproportionate.

The headlines suggesting a high protein diet is “as harmful as smoking” was not a specific finding of the study and could be seen as unnecessary fear-mongering. This is particularly of note given that the effects of a high protein diet were found to differ dramatically by age.

To be fair to the UK’s journalists, this comparison was raised in a press release, issued by the University of Southern California. Unfortunately this PR hype appears to have been taken at face value.


What kind of research was this?

This study looked at the relationship between the amount of protein consumed and subsequent risk of death among middle aged and older adults. It used data collected in a previous cross-sectional study and information from a national register of deaths in the US.

While the data used allowed researchers to identify what happened to people over time, this wasn’t the original purpose of the data collection. This means that some information on what happened to people may be missing, as researchers had to rely on national records rather than keeping close track of the individuals as part of the study.


What did the research involve?

The researchers had data on protein consumption for 6,381 US adults aged 50 and over (average age 65). They then identified which of these people died over the following 18 years (up to 2006) using national records. The researchers carried out analyses to see whether people who ate more protein in their diets were more likely to die in this period than those who ate less protein.

The information on protein consumption was collected as part the third National Health and Nutrition Examination Survey (NHANES). These surveys are designed to assess the health and nutritional status of people in the US. The participants are selected to be representative of the general US population. As part of the survey they reported their food and drink intake over the past 24 hours using a computerised system. The system then calculated how much of different nutrients they consumed.

Each person’s level of protein consumption was calculated as the proportion of calories consumed from protein. Protein intake was classed as:

  • High – 20% or more of calories from protein (1,146 people) 
  • Moderate – 10 to 19% of calories from protein (4,798 people) 
  • Low – less than 10% of calories from protein (437 people)

The researchers used the US National Death Index to identify any of the survey participants who died up to 2006, and the recorded cause of death. The researchers looked at whether proportion of calories consumed from protein was related to risk of death overall, or from specific causes. As well as overall deaths, they were also interested in deaths specifically from cardiovascular disease, cancer, or diabetes. The researchers also looked at whether the relationship differed in people aged 50-65 years, and older individuals, and whether it was influenced by fat, carbohydrate or animal protein intake.

The analyses took into account factors (confounders) that could influence the results, including:

  • age
  • ethnicity
  • education
  • gender
  • "disease status"
  • smoking history
  • participants’ dietary changes in the last year
  • participants’ attempted weight loss in the last year
  • total calorie consumption

The researchers also carried out studies to look at the effect of protein and their building blocks (amino acids) in yeast and mice.


What were the basic results?

On average, the participants consumed 1,823 calories over the day:

  • 51% from carbohydrates
  • 33% from fat
  • 16% from protein (11% from animal protein).

Over 18 years, 40% of participants died; 19% died from cardiovascular diseases, 10% died from cancer, and about 1% died from diabetes.

Overall, there was no association between protein intake and risk of death from any cause, or death from cardiovascular disease or cancer. However, moderate or high protein consumption was associated with an increased risk of death related to complications associated with diabetes. The authors noted that the number of people dying from diabetes-related causes was low, so larger studies were needed to confirm this finding.

The researchers found that results for death from any cause and from cancer seemed to vary with age. Among those aged 50-65, those who ate a high protein diet were 74% more likely to die during follow up than those who ate a low protein diet (hazard ratio (HR) 1.74, 95% confidence interval (CI) 1.02 to 2.97). People in this age group who ate a high protein diet were more than four times as likely to die from cancer during follow up than those who ate a low protein diet (HR 4.33, 95% CI 1.96 to 9.56).

The results were similar once the researchers took into account the proportion of calories consumed from fat and carbohydrates. Further analyses suggested that animal protein was responsible for a considerable part of this relationship, particularly for death from any cause.

However, the opposite effect of high protein intake was seen among those aged over 65. In this age group high protein intake was associated with:

  • a 28% reduction in the risk of death during follow up (HR 0.72, 95% CI 0.55 to 0.94)
  • a 60% reduction in the risk of death from cancer during follow up (HR 0.40, 95% CI 0.23 to 0.71)


How did the researchers interpret the results?

The researchers concluded that low protein intake during middle age followed by moderate to high protein consumption in older adults may optimise health and longevity.



This study has found a link between high protein intake and increased risk of death among people aged 50-65, but not older adults. There are some important points to bear in mind when thinking about these results:

  • The human data used was not specifically collected for the purpose of the current study. This meant that the researchers had to rely on the completeness of, for example, national data on deaths and causes of death. This may mean that deaths of some participants may have been missed.
  • Information on food intake was only collected for one 24-hour period, and this may not be representative of what people ate over time. Most people (93%) reported that it was typical of their diet at the time, but this may have changed over the 18 years of follow up.
  • The researchers took into account some factors that could affect results, but not others, such as physical activity.
  • Although the study was reasonably large, numbers in some comparisons were relatively low, for example, there were not many diabetes-related deaths and only 437 people overall ate a low protein diet. The broad confidence intervals for some of the results reflect this.
  • Many news sources have suggested that a high protein diet is “as bad for you” as smoking. This is not a comparison that is made in the research paper, therefore its basis is unclear. While we do need some protein in our diets, we don’t need to smoke, so this is not a helpful comparison.
  • While the authors suggested that people eat a low protein diet in middle age and switch to a high protein diet once they get older, it is not possible to say from the study whether this is what the older participants actually did, as their diets were only assessed once.
  • Ideally the findings need to be confirmed in other studies set up to specifically address the effects of higher protein diets, particularly the strikingly different results for different age groups.

While certain diet plans, such as the Atkins diet or the “caveman diet” have promoted the idea of eating a high-protein diet for weight loss, relying on a single type of energy source in your diet is probably not a good idea. Consumption of some high-protein foods such as red meat and processed meat is already known to be associated with increased risk of bowel cancer.


Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

High-protein diet 'as bad for health as smoking'. The Daily Telegraph, March 4 2014

Diets high in meat, eggs and dairy could be as harmful to health as smoking. The Guardian, March 4 2014

Eating too much meat and eggs is ‘just as bad as smoking’, claim scientists. The Independent, March 4 2014

Eating lots of meat and cheese in middle age is 'as deadly as SMOKING'. Daily Mail, March 4 2014

Eating lots of meat and cheese could be as bad for you as smoking, report reveals. Daily Mirror, March 4 2014

Meat And Cheese 'As Bad For You As Smoking'. Sky News, March 4 2014

Links to the science

Levine ME, Suarez JA, Brandhorst S, 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. Published online March 4 2014

Further reading

Press release

University of Southern California. Meat and cheese may be as bad as smoking. Published March 5 2013


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The 7 comments posted are personal views. Any information they give has not been checked and may not be accurate.

Ned Clack said on 17 March 2014

timerty suggests that it's the cooking method that makes animal protein carcinogenic. Once again we can thank the World Cancer Research Fund for http://tiny.cc/8ytucx which rates Argentina 49th out of the top 50 countries for all cancer incidence. In Argentina the 'national dish' is Asado, which consists of grilled meats, mostly beef. Average per capita consumption of beef alone is 1kg per head per week, but the people who are not developing cancer in Argentina today grew up at a time when the average Argentinean got through 2kg of beef every week, much of which was grilled.

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timerty said on 15 March 2014

The article is referring to meat-based protein and not plant-based protein.

Cooked meat contains heterocyclic amines(HCAs) and polycyclic aromatic hydrocarbons(PAHs).

Chemicals in Meat Cooked at High Temperatures and Cancer Risk


"-Heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) are chemicals formed when muscle meat, including beef, pork, fish, and poultry, is cooked using high-temperature methods, such as pan frying or grilling directly over an open flame.

-The formation of HCAs and PAHs is influenced by the type of meat, the cooking time, the cooking temperature, and the cooking method."

There is a strong correlation of Denmark's high grilled red meat consumption with its no.1 ranking for cancer rate in the world.

I wrote something about red meat consumption and its correlation to cancer a while ago.


Grilled red meat shops are popular in Denmark and Denmark has the highest number of meat-cooking grills per capita. This high consumption of red meat correlates with Denmark having the top spot for the rate of cancer for all countries in the world, which seems too high of a direct correlation even if their free medical system allows more people to be detected from the life-threatening disease. The exercise the Danes get from cycling don't seem to be able to offset the effects of the toxins that come from eating cooked meat.

(Even a Danish Professor from the Department of Public Health at a Danish University has advised on the cutting down of red meat)
Barbecue season: cut down on the red meat.

Cancer rate per 100,000 ranked 1st in the world
Data for cancer frequency by country

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papaleach said on 09 March 2014

This study resonates with much previous science and several
common sense historical observations:

1) Large populations in Asia that traditionally eat less animal protein than we do also avoid the high rates of cancer, heart disease , diabetes
and the rest that we suffer from;

2) Such populations, like the Japanese for example, begin to get more cancer and western diseases when they increasingly adopt more of the meaty
dairy western diet;

3) Our own populations’ rates of ‘diseases of affluence’ have
risen in tandem with increases in our animal food consumption over the last
century or so;

4) When forced by circumstances such as WWII to eat much less animal protein, and more plant protein, our own populations also experienced big
drops in heart disease etc, only to see the rates rise again with the end of rationing;

5) Small pockets of our populations who are vegetarian or vegan (such as the 7th day Adventists ) also have lower disease rates and longer life spans than the normal population;

6) Several practitioners of medicine by diet (principally plant
based whole foods) have proven recordsoof medicine by diet (principally plant based whole foods) have proven records of their success, sometimes with terminally ill patients surviving for decades. (For just two examples you could Google Caldwell Esselstein (Bill Clinton’s doctor) or Dr Roy Swank, who has a forty year success record with MS sufferers);
7) An eminent study into rural Chinese diets and disease rates in the 80s by world class researchers (whose team included Sir Richard Peto and Professor Colin Campbell ), recorded much the same findings as this one about the difference between plant protein and animal based proteins in relation to disease;
Finally, could I point out that ALL protein comes from plants? Protein from animals is second hand nutrition!

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TheFatEmperor said on 07 March 2014

The Protein Study and the conclusions contained within are close to worthless I'm afraid; jotted some notes on it here:


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Ned Clack said on 06 March 2014

If you think that eating red meat causes bowel cancer, the World Cancer Research Fund has a table on its statistics page that clearly challenges the hypothesis. http://www.wcrf-uk.org/research/cancer_statistics/bowel_cancer_rates.php shows that Argentina, until a few years ago the country with the highest per capita beef consumption in the world, lies 49th in the top 50 countries for bowel cancer.

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andyk105 said on 06 March 2014

As Zoe Harcombe on her blog 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’

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David Colquhoun said on 05 March 2014

Not a bad report, but why on earth didn't you mention the EPIC study? This was far bigger, 448,568 people from ten different European countries, followed for 12 years. It found no association whatsoever between red meat and all-cause mortality. If you want a proper assessment of the conflicting advice take a look at http://www.dcscience.net/?p=5935

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