By Dr. Mercola
The low-carb diet made its initial appearance as a weight loss aid some 25 years ago. At the time, most people recommended replacing non-vegetable carbohydrates with high amounts of protein, and these low-carb, high-protein diets (such as Atkins) worked quite well for the purpose of shedding weight.
Indeed, eating more protein is still frequently recommended for weight loss as it does help reduce appetite,1 and may slow down digestion of carbohydrates, thereby preventing harmful blood sugar spikes.2 The problem with this recommendation is that eating too much protein also has significant drawbacks.
One of the most significant problems you may encounter when eating excess protein is that it stimulates the most important nutrient signaling pathway in your body: mTOR (mammalian target of rapamycin).
MTOR plays a crucial role in the aging process and cancer formation. Unfortunately, to this day, few people are fully aware of and understand this influence.
When the mTOR pathway is stimulated, it promotes growth — including cancer cell growth — rather than regeneration. MTOR activation also inhibits cellular and mitochondrial authophagy, or the destruction of damaged cells and mitochondria.
When you limit protein to just what your body needs, mTOR remains largely inhibited, which helps minimize your chances of cancer growth.
A far healthier strategy is to replace unnecessary net carbs with healthy fats, as fats do not have the adverse metabolic effects associated with both carbs and protein. Unfortunately, dietary fat has been wrongly demonized as promoting obesity and heart disease.
I've discussed the benefits of diets high in healthy fats and the dangers of excess protein for a number of years now, and the notion that restricting protein and increasing fat are important factors can affect health is finally starting to gain recognition.
Too Much of a Good Thing Can Be Bad
Protein loading has been touted as a great way to improve muscle building and facilitate weight loss, resulting in a wide array of protein-rich foods and supplements, from shakes to snack bars that provide hefty amounts.
Granted, your body certainly requires protein. Amino acids from protein are the primary building blocks for muscles, bones and enzymes. As you age, and during pregnancy, consuming sufficient amounts of high-quality protein is especially important.
That said, there IS an upper limit to how much protein your body can actually use, and anything exceeding that requirement will simply activate mTOR, thereby speeding up the aging process and related health problems, including your risk for cancer and neurodegenerative diseases.
The recommended daily intake (RDI) is 46 grams of protein for women and 56 grams for men — an amount easily achieved by eating a moderate amount of meat, fish, dairy, beans or nuts every day. For example, 1 cup of chopped chicken will provide you with 44 grams of protein.
Meanwhile, American men consume close to 100 grams of protein each day.3 Eating nearly double the protein most need for optimal health can have significant adverse health consequences. As reported by The New York Times:4
"'People think carbs are the enemy, protein is your friend,' said Eleanor Dwyer, a research analyst … and 'that any health concerns are overblown.' Experts note, however, that there is only so much protein the body can use.
'The body only digests and absorbs a certain amount of protein at every meal,' about 20 to 40 grams, said Jim White, a registered dietitian and exercise physiologist who spoke on behalf of the Academy of Nutrition and Dietetics.
'People think that if they fill up with protein, it will be a magic bullet, whether for weight loss or to get in better shape and build muscle — but that's not proving to be true. You can eat 300 grams of protein a day, but that doesn't mean you'll put on more muscle than someone who takes in 120 grams a day' … "
High Protein Adversely Affects Your Insulin and Leptin
In addition to stimulating mTOR, protein also affects your insulin, and leptin. Dietary fats do not affect any of these. As a result, a low-carb, high-protein diet may still be troublesome if you're struggling with obesity, insulin resistance or diabetes.
Indeed, many studies have found an association between chronic high protein intake and an elevated risk of diabetes.
This was recently demonstrated in a short-term trial5 published in Cell Reports, in which older women who lost weight on a high-protein diet failed to reap the benefits typically associated with weight loss, such as improved insulin sensitivity. As noted by the authors:
"High-protein intake during weight loss therapy is often recommended because it reduces the loss of lean tissue mass. However, high-protein intake could have adverse effects on metabolic function, because protein ingestion reduces postprandial insulin sensitivity."
High Protein Improves Fat Loss, but Not Insulin Resistance
In this study, the researchers compared the effects of 0.8 grams of protein per kilo (kg) per day versus 1.2 grams of protein/kg/day on muscle insulin action in obese postmenopausal women.
"We found that high-protein intake reduced the weight loss-induced decline in lean tissue mass by ∼45 percent," the researchers note. In other words, while both groups lost the same amount of weight overall, the high protein group lost more body fat than muscle mass.
"However, high-protein intake also prevented the weight loss-induced improvements in muscle insulin signaling and insulin-stimulated glucose uptake, as well as the weight loss-induced adaptations in oxidative stress and cell structural biology pathways.
Our data demonstrate that the protein content of a weight loss diet can have profound effects on metabolic function and underscore the importance of considering dietary macronutrient composition during weight loss therapy for people with obesity."
Dan Pardi published a long analysis6 of the Cell Reports study, dissecting the reasons why women on a high-protein diet would lose higher amounts of body fat yet experience worsening insulin sensitivity.
Pardi is a proponent of high-protein diets, and while he manages to make a case to still support high protein while acknowledging that the study clearly showed worse insulin resistance in those who consumed higher protein levels, he completely fails to address protein's impact on mTOR.
This should be a serious consideration for anyone interested in optimizing their health. After all, why trade weight loss for an increased risk of cancer when you can lose weight without taking such risks?
Chronic High-Protein Diets May Raise Your Risk for Cancer
It may not be entirely intuitive, but eating more protein than your body actually requires will convert most of the excess into sugar, and then body fat. This is very similar to what happens when you eat a high-carb diet.
Increased blood sugar levels can also feed pathogenic bacteria and yeast, such as Candida albicans (candidiasis). It can also serve as fuel for cancer cell growth. As noted by Dr. Walter Willett, chairman of the department of nutrition at the Harvard T. H. Chan School of Public Health:7
"One of the benefits and concerns about high protein intake, especially animal protein, is that it tends to make cells multiply faster. That's good in early life, when you're a growing child. But in later life, this is one of the fundamental processes that increase the risk of cancer."
In one 2014 study8 involving more than 6,380 American adults over the age of 50, those who ate a diet high in animal protein:
- Had a 75 percent increase in overall mortality over the course of 18 years
- Were 400 percent more likely to die of cancer than those who restricted their animal protein. (According to the authors, this association vanished when the protein was derived from plants)
- Had a 500 percent increase in diabetes across all ages
The only people who benefited from a high-protein diet were seniors over the age of 65. In this age group, high amounts of animal protein were associated with reduced cancer and overall mortality risk. According to the authors:
"These results suggest that low protein intake during middle age followed by moderate- to high-protein consumption in old adults may optimize healthspan and longevity."
Again, while none of the media articles reporting these findings delve into the actual mechanism behind this phenomenon, the cancer connection to excess protein is directly related to the stimulation of mTOR. This is partially related to the fact that the mTOR pathway has only recently been discovered and is not widely appreciated by clinicians or the media.
Why Protein Cycling May Be Helpful
Other studies have shown that high-protein diets fail to preserve muscle mass over the long term. It can also put your health at risk by stressing your kidneys,9 thereby raising your risk for kidney disease. Dehydration10 and leaching of important bone minerals are also risks associated with chronic excessive protein intake.
Newer studies have also shed light on how protein restriction impacts longevity. While animal studies have established that calorie restriction promotes longevity, the latest science suggests this phenomenon may actually be the result of reduced protein intake — specifically, reduced intake of the amino acid methionine, which is high in meats.11 In fact, animal research12,13 has revealed protein restriction alone may increase lifespan by as much as 20 percent.
Other studies suggest it may be the balance of amino acids that is the key, especially with other amino acids like glycine that may actually help lower methionine levels.
How can you use this information to your advantage? One helpful strategy would be to implement protein cycling, where you intermittently cycle through periods of low protein and higher protein intake. Replicating the ancestral pattern of going through feasts and famines can help normalize your amino acid levels. That is one of the benefits of intermittent fasting. Bone broth may be particularly useful as it is especially high in glycine that helps lower your methionine.
How Much Protein Is Too Much?
According to the Institute of Medicine, you need at least 10 percent of your daily calories from protein, but not more than 35 percent.
However, research14 by Valter Longo, Ph.D., professor of gerontology and biological sciences at the University of Southern California, shows that people who get 20 percent or more of their daily calories from protein have a 400 percent higher cancer rate compared to those who get only 10 percent of daily calories from protein. The general recommendations for protein are:15,16
Babies: 10 grams/day
School-aged children: 19 to 34 grams/day
Teenage boys: up to 52 grams/day
Teenage girls: 46 grams/day
Adult men: 56 grams/day
Adult women: 46 grams/day (pregnant and breastfeeding women: 71 grams/day)
However, research suggests specificity and precision are really key when it comes to protein, and since the majority of Americans are overweight, I prefer using a more precise formula that calculates your protein requirement based on LEAN bodyweight (i.e. muscle weight) only. This is far more relevant to your biological needs than age and gender.17
This formula calls for about 0.5 gram of protein per pound of lean body mass (or for the Europeans: 1 gram per kg of lean body mass). Pregnant women and those who are aggressively exercising or competing should have about 25 percent more.
To determine your lean body mass, simply subtract your percent body fat from 100. For example, if you have 20 percent body fat, then you have 80 percent lean body mass. Just multiply that percentage (in this case, 0.8) by your current weight to get your lean body mass in pounds or kilos. In the above example, if you weighed 160 pounds, 0.8 multiplied by 160 equals 128 pounds of lean body mass. Using the "0.5 gram of protein" rule, you would need about 64 grams of protein per day.
Translating Ideal Protein Requirements into Foods
Substantial amounts of protein can be found in meat, fish, eggs, dairy products, legumes, nuts and seeds. Some vegetables, such as broccoli, also contain generous amounts of protein.18 To determine whether or not you're getting too much protein, simply calculate your body's requirement based on your lean body mass, as described above, and write down everything you eat for a few days. Then, calculate the amount of daily protein you've consumed from all sources.
If you're currently averaging a lot more than the optimal 0.5 gram of protein per pound of lean body mass, adjust downward accordingly. You could use the chart below or simply Google the food you want to know and you will quickly find the grams of protein in that food.
Red meat, pork, poultry and seafood average 6 to 9 grams of protein per ounce.
An ideal amount for most people would be a 3-ounce serving of meat or seafood (not 9- or 12- ounce steaks!), which will provide about 18 to 27 grams of protein
Eggs contain about 6 to 8 grams of protein per egg. An omelet made from two eggs would give you about 12 to 16 grams of protein.
If you add cheese, you need to calculate that protein in as well (check the label of your cheese)
Seeds and nuts contain on average 4 to 8 grams of protein per quarter cup
Cooked beans average about 7 to 8 grams per half cup
Cooked grains average 5 to 7 grams per cup
Most vegetables contain about 1 to 2 grams of protein per ounce
Beware that many nuts, while high in healthy fats, are also high in protein. Macadamia nuts have the highest fat and lowest protein and carb content of any nut, making them an ideal choice for snacking. Pecans and pine nuts are also high in healthy fats while being lower in protein.
Be Mindful of Quality When Selecting Meats
The quality of the meat you eat is as important as the quantity. As a general rule, the only meat I recommend eating is organically raised grass-fed and grass-finished meats.
The same goes for dairy and eggs. Meat from pastured or grass-fed animals is far superior to that from animals raised in confined animal feeding operations (CAFOs), which is frequently contaminated with herbicides, pesticides, hormones, antibiotics and other drugs, as well as GMOs from the genetically engineered (GE) grains these animals typically consume.
Researchers are even suggesting that CAFO beef may be spreading slow-acting prion infection causing Alzheimer's disease. The damage is identical to that seen in Mad Cow disease, except for the rate of speed with which the infection destroys your brain and causes death.
In 2009, a joint research project between the U.S. Department of Agriculture (USDA) and Clemson University determined a total of 10 key areas where grass-fed is better for human health than grain-fed beef. In a side-by-side comparison, they determined that grass-fed beef was superior in the following ways:19
Higher in total omega-3s
A healthier ratio of omega-6 to omega-3 fatty acids (1.65 vs 4.84)
Higher in CLA (cis-9 trans-11), a potential cancer fighter
Higher in vaccenic acid (which can be transformed into CLA)
Higher in the B-vitamins thiamin and riboflavin
Higher in the minerals calcium, magnesium and potassium
Higher in vitamin E (alpha-tocopherol)
Higher in beta-carotene
The Type of Fats You Eat Influence Your Mortality Risk
As mentioned, another part of the healthy diet equation is replacing net carbs with healthy fats rather than protein. Fats will not stimulate mTOR or raise your insulin or leptin levels. However, all fats are not made equal, and as recently revealed by Harvard researchers, replacing bad fats with healthy ones can reduce your risk of dying by more than 25 percent.20 As reported by CNN:21
"… [A] new study from Harvard … analyzed the eating habits of more than 126,000 men and women over a 32-year period. And some fats were better than others from [sic] protecting against specific diseases … Omega-3 fatty acids (those found in fish and some nuts and seeds) can help strengthen your heart and possibly your mental well-being, too. And the monounsaturated fats in olive oil (as well as nuts and avocados) can also cut your risk of heart disease …
Previous thinking also cautioned against foods high in cholesterol … but that's no longer the case. Dietary cholesterol doesn't necessarily raise the 'bad' cholesterol levels in your body … Instead, it can elevate HDL or the 'good' kind. One caveat: Trans fats and linoleic acid (found in vegetable oils) can harm your health.
So steer clear of partially hydrogenated and hydrogenated oils, like canola, as well as packaged foods like cream-filled candies, frozen pizza and margarine. Sometimes, the nutrition label doesn't show trans fat, so look for hydrogenated oils on the ingredients list."
Normalize Your Protein Intake to Optimize Your Health
Pinning down the ideal amount of protein can be tricky business, with plenty of variables adding to the confusion. Still, I believe calculating your need based on lean body weight is a good start, and 0.5 grams of protein per pound of lean body mass is likely sufficient for most. Athletes, pregnant or breastfeeding women and possibly the elderly may need around 25 percent more.
I strongly encourage you to do a careful analysis of precisely how much protein you are eating every day. The results may surprise you, as I'm sure many are consuming more than 100 grams per day, and very few people would need that much. You would have to be a 6 foot 4 inch, 225-pound athlete with 10 percent body fat to need that much. If you are a competitive athlete, higher protein levels may help you achieve your athletic goals but will likely have a negative impact on your long-term health.
And remember, while higher protein may aid weight loss, the drawbacks are manifold, and can easily outweigh this benefit. A ketogenic diet is likely a far safer alternative if you need to lose weight. Shifting over to higher quality protein sources is also important, as factory farmed animal foods come with drawbacks that go beyond the issue of protein.
Optimizing protein intake is a crucial part in getting your body to burn fat as your primary fuel, but I go into far greater detail on how to do this in my new book, "Fat for Fuel," which comes out in May 2017.