Do High Protein Diets Cause Cancer?

Written by Dr. Steve Chaney on . Posted in Food and Health, Issues

How Much Protein Should We Eat?

Author: Dr. Stephen Chaney

Animal Protein FoodsThe recent headlines suggesting that high protein diets may cause cancer, diabetes and premature death in middle aged Americans are downright scary. You are probably asking yourself:

  • “Is this new information?”
  • “Does this apply to me?”
  • “Should I radically change what I eat?”

In this issue of “Health Tips From the Professor” I will address each of these questions.

Do High Protein Diets Cause Cancer?

The study in question (Levine et al., Cell Metabolism, 19: 407-417, 2014) suggested that high protein diets were associated with increased risk of cancer, diabetes and premature death in Americans in the 50-65 age range. I will touch on all three of these observations, but it is the increased risk of cancer that generated the most headlines – and the most concern (The consequences of diabetes take years to manifest, and death seem to be a more distant concern for most people. Cancer is immediate and personal).

The study looked at 6,381 adults aged 50 and older (average age 65) from the NHANES III data base. (NHANES is a comprehensive database collected by the Centers for Disease Control and Prevention that consists of surveys and physical examinations and is designed to be representative of the health and nutritional status of the US population.)

The data collected consisted of a single diet questionnaire conducted when the subjects were enrolled in the study. Based on the diet questionnaire the authors of the study divided the group into those with low protein intake (<10% of calories), those with moderate protein intake (10-19% of calories) and those with high protein intake (>20% of calories). Overall death and mortality from various diseases over the next 18 years was obtained by linking the NHANES data with the National Death Index.

Based on preliminary data suggesting that the age of the population might influence the results (I won’t go into details here) the authors of the study decided to subdivide the dataset into people aged 50-65 and people over 65. When they did that, they came to the following conclusions:

1)     In the 50-65 age group diets high in animal protein were associated with a:

  • 45% increase in overall mortality
  • 4-fold increase in cancer death risk
  • 4-fold increase in diabetes death risk.

Diets with moderate protein intake were associated with intermediate increases in risk. Surprisingly, there was no increase in cardiovascular disease risk.

Protein Shakes2)     When they looked at people in the 50-65 age group consuming diets high in vegetable protein:

  • the increased overall mortality and increased in cancer mortality disappeared
  • the increased diabetes mortality was still seen.

3)     In the 65+ age group high protein diets were associated with a:

  • 28% decrease in overall mortality
  • 60% decrease in cancer mortality.

The increased risk of diabetes related deaths was still observed. The authors did not distinguish between animal and vegetable protein in the over 65 age group.

All of that may seem to be a bit too complicated. At the risk of gross oversimplification I would summarize their message as follows:

  • Diets high in animal protein may be bad for you if you are in the 50-65 age range, but might actually be good for you if you are over 65.
  • Diets high in vegetable protein appear to be good for anyone over age 50 (The study didn’t look at younger age groups).

Is This New Information?

Let’s start by assuming that the conclusions of the authors are correct (more about that below).

When you boil their message down to its simplest components, the information isn’t particularly novel.

  • The idea that vegetable proteins may be better for you than animal proteins has been around for decades. There are a number of studies suggesting that diets high in animal protein increase the risk of cancer, heart disease, diabetes and overall death – although it is still not clear whether it is the animal protein itself or some other characteristic of populations consuming mostly animal protein that is the culprit.
  • Evidence has been accumulating over the past decade or so that protein needs increase as we age, so it is not surprising that this study found high protein diets to be beneficial for those of us over age 65.

What Do Other Experts Say?

ScientistSince this study has been released it has been roundly criticized by other experts in the field. Let me sum up their four main criticisms and add one of my own.

1)     The protein intake data were based on a single dietary survey taken at the beginning of an 18 year study. The authors stated that a single dietary survey has been shown to be a pretty accurate indicator of what an individual is eating at the time of the survey. However, it is problematic to assume that everyone’s diet remained the same over an 18 year period.

2)     The choice of less than 10% of calories from protein is also problematic. According to the Institute of Medicine standards anything below 10% is defined as inadequate protein intake, which can have long term health consequences of its own.

More importantly, only 7% of the population being studied (437 individuals) fell into this group. This is the baseline group (or put another way, the denominator for all of the comparisons). The conclusions of this study were based on comparing the other two groups to this baseline, and there were too few individuals in this group to be confident that the baseline is accurate.

This does not necessarily invalidate the study, but it does decrease confidence in the size of the reported effect – so forget the reported numbers like 45% increase in mortality and 4-fold increase in cancer deaths. They probably aren’t accurate.

3)     The number of people in this study who died from diabetes was exceedingly small (68 total) and most of them already had diabetes when the study began. The experts concluded that the numbers were simply too low to draw any conclusions about protein intake and diabetes related deaths, and I agree with them.

4)     While the study controlled for fat intake and carbohydrate intake, it did not control for weight. That is a huge omission. Overweight is associated with increased risk of cancer, diabetes and death, and vegetarians tend to weigh less than non-vegetarians.

5)     I would add that there are many other differences between vegetarians and non- vegetarians that could account for most of the differences reported between diets high in animal and vegetable protein. For example:

  • Vegetarians tend to be more health conscious and thus they tend to exercise more, consume more fiber, consume more fruits and vegetables, consume less fried food, and consume less processed and convenience foods – all of which are associated with decreased risk of cancer, diabetes and death.

The Bottom Line:

This is not a particularly strong study. Nor is it particularly novel. In fact, when you strip away the scary headlines and focus on what the data really show, the conclusions aren’t that different from what nutrition experts have been saying for years.

1)     This study suggests that if you are in the 50-65 age range, diets high in animal protein may not be good for you (this study focused on increased risk of cancer death and overall mortality. Other studies have suggested that diets high in animal protein may increase the risk of cardiovascular death).

This is not a new idea. These data are consistent with a number of other studies. However, none of these studies adequately assess whether the increased risk is from the animal protein alone or from other characteristics of populations that consume a lot of animal protein.

2)     This study also suggests that diets high in vegetable protein do not increase either cancer risk or all cause mortality. That’s also not new information. We’ve known for years that people who consume primarily vegetable protein appear to be healthier. Once again, it is not clear whether it is the vegetable protein itself that is beneficial or whether the benefit is due to other characteristics of populations who consume a lot of vegetable protein.

3)     Does that mean that you need to become a vegetarian? It probably reflects my personal bias, but I am reminded of a Woody Allen Quote: “Vegetarians don’t live longer. It just seems that way”. I am also encouraged by studies suggesting that most of the health benefits of vegetarianism can be achieved by diets that consist of around 50% vegetable protein.

I would never discourage anyone from becoming a vegetarian, but if you aren’t ready for that, I would highly recommend that you aim for at least 50% vegetable protein in your diet.

4)     Finally, this study suggests that a high protein diet is beneficial for people over 65. This is also not a completely novel idea. It is consistent with a lot of recent research.

My advice to those of you who, like me, are over 65 is to pay attention to high protein foods and make sure that they are an important part of your diet. I’m not suggesting that you go for the double bacon cheeseburger just because you are over 65. I would still aim for a significant percentage of vegetable protein as a part of a healthy diet at any age.

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

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Comments (2)

  • Robert D. Munson, Ph.D., St. Paul, MN

    |

    Have you seen the documentary video, Forks Over Knives? In one part of it, as I recall, in a cancer study,dietary protein from milk was consumed at 5% and at 20%. Under the 5% cancer tumors shrunk, but grew under the 20% level. Have you reviewed Dr. Joel Fuhrman’s video, 3 Steps to Incredible Health , or Immunity Solutions? He leans heavily on various vegetables, especially salads (as a main meal).

    I believe that in many cases we do not pay enough attention to the cation make up of our diet. In general, potassium or magnesium are often neglected. Various elements activate enzymes, and influence cellular structures, such as the endoplasmic rheticulum, where cellular proteins are programmed. K/Na relationships are important in that regard. Cations also influence cytoplasmic streaming which influence rates of reaction within cells. Most of our diets in the U.S. are way to high in Na, especially in process and fast food operations.

    I really appreciate your analyses of various subjects. Thank you so much for all you do. I appreciate your discussion of on Cancer last evening.

    Reply

    • Dr. Steve Chaney

      |

      Dear Dr. Munson,
      I have seen “forks Over Knives”. There is a lot of good information in there. I think we could all benefit from a diet that included more fresh fruits and vegetables. I also believe in eating all things in moderation. For example, in the study you referred to 20% of protein from milk would be a lot of milk. It would be an unbalanced diet.

      You are also right on about mineral imbalances, We get far too much sodium in our diets and far too little potassium, magnesium and essential trace minerals.

      Dr. Chaney

      Reply

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Latest Article

A Low Carb Diet and Weight Loss

Posted January 15, 2019 by Dr. Steve Chaney

Do Low-Carb Diets Help Maintain Weight Loss?

Author: Dr. Stephen Chaney

 

low carb dietTraditional diets have been based on counting calories, but are all calories equal? Low-carb enthusiasts have long claimed that diets high in sugar and refined carbs cause obesity. Their hypothesis is based on the fact that high blood sugar levels cause a spike in insulin levels, and insulin promotes fat storage.

The problem is that there has been scant evidence to support that hypothesis. In fact, a recent meta-analysis of 32 published clinical studies (KD Hall and J Guo, Gastroenterology, 152: 1718-1727, 2017 ) concluded that low-fat diets resulted in a higher metabolic rate and greater fat loss than isocaloric low-carbohydrate diets.

However, low-carb enthusiasts persisted. They argued that the studies included in the meta-analysis were too short to adequately measure the metabolic effects of a low-carb diet. Recently, a study has been published in the British Medical Journal (CB Ebbeling et al, BMJ 2018, 363:k4583 ) that appears to vindicate their position.

Are low carb diets best for long term weight loss?

Low-carb enthusiasts claim the study conclusively shows that low-carb diets are best for losing weight and for keeping it off once you have lost it. They are saying that it is time to shift away from counting calories and from promoting low-fat diets and focus on low-carb diets instead if we wish to solve the obesity epidemic. In this article I will focus on three issues:

  • How good was the study?
  • What were its limitations?
  • Are the claims justified?

 

How Was The Study Designed?

low carb diet studyThe investigators started with 234 overweight adults (30% male, 78% white, average age 40, BMI 32) recruited from the campus of Framingham State University in Massachusetts. All participants were put on a diet that restricted calories to 60% of estimated needs for 10 weeks. The diet consisted of 45% of calories from carbohydrate, 30% from fat, and 25% from protein. [So much for the claim that the study showed low-carb diets were more effective for weight loss. The diet used for the weight loss portion of the diet was not low-carb.]

During the initial phase of the study 161 of the participants achieved 10% weight loss. These participants were randomly divided into 3 groups for the weight maintenance phase of the study.

  • The diet composition of the high-carb group was 60% carbohydrate, 20% fat, and 20% protein.
  • The diet composition of the moderate-carb group was 40% carbohydrate, 40% fat, and 20% protein.
  • The diet composition of the low-carb group was 20% carbohydrate, 60% fat, and 20% protein.

Other important characteristics of the study were:

  • The weight maintenance portion of the study lasted 5 months – much longer than any previous study.
  • All meals were designed by dietitians and prepared by a commercial food service. The meals were either served in a cafeteria or packaged to be taken home by the participants.
  • The caloric content of the meals was individually adjusted on a weekly basis so that weight was kept within a ± 4-pound range during the 5-month maintenance phase.
  • Sugar, saturated fat, and sodium were limited and kept relatively constant among the 3 diets.

120 participants made it through the 5-month maintenance phase.

 

Do Low-Carb Diets Help Maintain Weight Loss?

low carb diet maintain weight lossThe results were striking:

  • The low-carb group burned an additional 278 calories/day compared to the high-carb group and 131 calories/day more than the moderate-carbohydrate group.
  • These differences were even higher for those individuals with higher insulin secretion at the beginning of the maintenance phase of the study.
  • These differences lead the authors to hypothesize that low-carb diets might be more effective for weight maintenance than other diets.

 

What Are The Pros And Cons Of This Study?

low carb diet pros and consThis was a very well-done study. In fact, it is the most ambitious and well-controlled study of its kind. However, like any other clinical study, it has its limitations. It also needs to be repeated.

The pros of the study are obvious. It was a long study and the dietary intake of the participants was tightly controlled.

As for cons, here are the three limitations of the study listed by the authors:

#1: Potential Measurement Error: This section of the paper was a highly technical consideration of the method used to measure energy expenditure. Suffice it to say that the method they used to measure calories burned per day may overestimate calories burned in the low-carb group. That, of course, would invalidate the major findings of the study. It is unlikely, but it is why the study needs to be repeated using a different measure of energy expenditure.

#2: Compliance: Although the participants were provided with all their meals, there was no way of being sure they ate them. There was also no way of knowing whether they may have eaten other foods in addition to the food they were provided. Again, this is unlikely, but cannot be eliminated from consideration.

#3: Generalizability: This is simply an acknowledgement that the greatest strength of this study is also its greatest weakness. The authors acknowledged that their study was conducted in such a tightly controlled manner it is difficult to translate their findings to the real world. For example:

  • Sugar and saturated fat were restricted and were at very similar levels in all 3 diets. In the real world, people consuming a high-carb diet are likely to consume more sugar than people in the other diet groups. Similarly, people consuming the low-carb diet are likely to consume more saturated fat than people in the other diet groups.
  • Weight was kept constant in the weight maintenance phase by constantly adjusting caloric intake. Unfortunately, this seldom happens in the real world. Most people gain weight once they go off their diet – and this is just as true with low-carb diets as with other diets.
  • The participants had access to dietitian-designed prepared meals 3 times a day for 5 months. This almost never happens in the real world. The authors said “…these results [their data] must be reconciled with the long-term weight loss trials relying on nutrition education and behavioral counseling that find only a small advantage for low carbohydrate compared with low fat diets according to several recent meta-analyses.” [I would add that in the real world, people do not even have access to nutritional education and behavioral modification.]

 

low carb diet and youWhat Does This Study Mean For You?

  • This study shows that under very tightly controlled conditions (dietitian-prepared meals, sugar and saturated fat limited to healthy levels, calories continually adjusted so that weight remains constant) a low-carb diet burns more calories per day than a moderate-carb or high-carb diet. These findings show that it is theoretically possible to increase your metabolic weight and successfully maintain a healthy weight on a low-carb diet. These are the headlines you probably saw. However, a careful reading of the study provides a much more nuanced viewpoint. For example, the fact that the study conditions were so tightly controlled makes it difficult to translate these findings to the real world.
  • In fact, the authors of the study acknowledged that multiple clinical studies show this almost never happens in the real world. These studies show that most people regain the weight they have lost on low-carb diets. More importantly, the rate of weight regain is virtually identical on low-carb and low-fat diets. Consequently, the authors of the current study concluded “…translation [of their results to the real world] requires exploration in future mechanistic oriented research.” Simply put, the authors are saying that more research is needed to provide a mechanistic explanation for this discrepancy before one can make recommendations that are relevant to weight loss and weight maintenance in the real world.
  • The authors also discussed the results of their study in light of a recent, well-designed 12-month study (CD Gardener et al, JAMA, 319: 667-669, 2018 ) that showed no difference in weight change between a healthy low-fat versus a healthy low-carbohydrate diet. That study also reported that the results were unaffected by insulin secretion at baseline. The authors of the current study noted that “…[in the previous study] participants were instructed to minimize or eliminate refined grains and added sugars and maximize intake of vegetables. Probably for this reason, the reported glycemic load [effect of the diet on blood sugar levels] of the low-fat diet was very low…and similar to [the low-carb diet].” In short, the authors of the current study were acknowledging that diets which focus on healthy, plant-based carbohydrates and eliminate sugar, refined grains, and processed foods may be as effective as low-carb diets for helping maintain a healthy weight.
  • This would also be consistent with previous studies showing that primarily plant-based, low-carb diets are more effective at maintaining a healthy weight and better health outcomes long-term than the typical American version of the low-fat diet, which is high in sugar and refined grains. In contrast, meat-based, low-carb diets are no more effective than the American version of the low-fat diet at preventing weight gain and poor health outcomes. I have covered these studies in detail in my book “Slaying The Food Myths.”

Consequently, the lead author of the most recent study has said: “The findings [of this study] do not impugn whole fruits, beans and other unprocessed carbohydrates. Rather, the study suggests that reducing foods with added sugar, flour, and other refined carbohydrates could help people maintain weight loss….” This is something we all can agree on, but strangely this is not reflected in the headlines you may have seen in the media.

The Bottom Line

 

  • A recent study compared the calories burned per day on a low-carb, moderate-carb, and high-carb diet. The study concluded that the low-carb diet burned significantly more calories per day than the other two diets and might be suitable for long-term weight control. If confirmed by subsequent studies, this would be the first real evidence that low-carb diets are superior for maintaining a healthy weight.
  • However, the study has some major limitations. For example, it used a methodology that may overestimate the benefits of a low-carb diet, and it was performed under tightly controlled conditions that can never be duplicated in the real world. As acknowledged by the authors, this study is also contradicted by multiple previous studies. Further studies will be required to confirm the results of this study and show how it can be applied in the real world.
  • In addition, the kind of carbohydrate in the diet is every bit as important as the amount of carbohydrate. The authors acknowledge that the differences seen in their study apply mainly to carbohydrates from sugar, refined grains, and processed foods. They advocate diets with low glycemic load (small effects on blood sugar and insulin levels) and acknowledge this can also be achieved by incorporating low-glycemic load, plant-based carbohydrates into your diet. This is something we all can agree on, but strangely this is not reflected in the headlines you may have seen in the media.
  • Finally, clinical studies report averages, but none of us are average. When you examine the data from the current study, it is evident that some participants burned more calories per hour on the high-carb diet than other participants did on the low carb diet. That reinforces the observation that some people lose weight more effectively on low-carb diets while others lose weight more effectively on low-fat diets. If you are someone who does better on a low-carb diet, the best available evidence suggests you will have better long-term health outcomes on a primarily plant-based, low-carb diet such as the low-carb version of the Mediterranean diet.

For more details read the article above.

 

 

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

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