Will a high-protein diet harm your health? The real story on the risks (and rewards) of eating more protein.

Will a high-protein diet harm your health? The real story on the risks (and rewards) of eating more protein.

Will protein help me lose weight? Should I eat it at every
meal? Could too much damage my kidneys? At Precision Nutrition, our
inbox is filled with questions about the pros and cons of eating
more protein. In this article we’ll set the record straight, so
you can finally separate the facts from the fiction.


Maybe you’re a protein promoter.

You buy protein powder in “bucket with a handle” format. You
know the protein counts of every food you eat.

After every workout, you jam those amino acids into your cells.
You swear you can feel them getting swole.

Or maybe you’re a protein avoider.

Maybe you’ve heard bad things.

Like: Protein will damage your kidneys.

Or: Protein will give you cancer.

Or simply: We all eat too much protein.

Maybe you want to lose fat. Or gain muscle. Or be healthy.

You just want to do the right thing and eat
better. But with conflicting information about protein,
you don’t know what to think.

Or, if you’re a fitness and nutrition coach, you’re
wondering how the heck to clear up the confusion about protein
among your clients.

Let’s get into it.
In this article, we’ll explore:

What are high-protein diets?
What does the evidence say about high-protein diets and
Does protein source matter?
How much protein is right for me?

How to read this article

If you’re just curious about high-protein

Feel free to skim and learn whatever you like.

If you want to change your body and/or

You don’t need to know every detail. Just get the general
Check out our advice at the end.

If you’re an athlete interested in

Pay special attention to the section on athletic
Check out our advice for athletes at the end.

If you’re a fitness pro, or interested in geeking out
with nutritional science:

We’ve given you some “extra credit” material in sidebars
Check out our advice for fitness pros at the end.

Why protein?

A quick intro if you aren’t a nutrition pro:

Protein is one of the three main
macronutrients that makes up the food we eat. (The
other two are fat and carbohydrate.)

Protein itself is made up of amino acids.

Amino acids are the building blocks for most
stuff in our bodies. They’re like Legos that can be broken down
and re-assembled in different ways.

Unlike extra fat (which we can store very easily on our bums
and bellies), we don’t store lots of extra amino
acids. Protein is always getting used, recycled, and
sometimes excreted.

If we don’t get enough protein, our body will start
to plunder it from parts that we need, such as our

So we have to constantly replenish protein by
eating it.

We need protein.

Protein is so important that without it, we die or become
seriously malnourished.

(This protein-deficiency disease is known as kwashiorkor, and we
often see it in people who have suffered famines or who are living
on a low-protein diet.)

All your enzymes and cell transporters; all your blood
transporters; all your cells’ scaffolding and structures; 100
percent of your hair and fingernails; much of your muscle, bone,
and internal organs; and many hormones are made of mostly protein.
Hence, protein enables most of our bodies’ functions.

Put simply, you are basically a pile of protein.

No protein, no you.

How much protein do we need?

Short answer: It depends.

Let’s look first at the current Recommended Daily Allowance

The RDA for protein is  0.8 g/kg (0.36 g/lb) — the more you
weigh, the more protein you need:

A 150-lb (68 kg) person would need 68 x 0.8,
or about 54 grams of protein a day.

A 200-lb (91 kg) person would need 91 x 0.8,
or about 73 grams of protein a day.

That generally works out to about 10 percent of daily calories
coming from protein.


RDAs were originally developed as a way to prevent
malnutrition — to represent the minimum amount of a nutrient we
need to not die (or get sick).

“You’re not dead” is not the same thing as “You’re
kicking ass.”
The RDA for surviving may be different than what we need to

The RDA is also a very general recommendation. It doesn’t take
other things into account, such as:

How much total energy (i.e. calories) we eat or need
Our carbohydrate intake
When we eat the protein
Our biological sex
Our age
How active we are
What activities we do
How “eco-friendly” various protein sources are

The Institute of Medicine (US) suggests a huge range in
individual protein requirements — from 0.375 g/kg to 1.625 g/kg
body weight (0.17 to 0.74g/lb body weight).

In other words, our hypothetical 150-lb person might have
protein needs ranging from 26 to 111 grams per day.

Well that narrows it down nicely, doesn’t it!?

Let’s take a deeper look: Amino acids

Protein in our food is made up of many different building
blocks, or amino acids.

Most people focus on Recommended Daily Allowance (RDA) for total
protein, but they don’t think about how much of each amino acid
they might need.

If your diet isn’t varied enough, you may be eating
enough total protein, but not enough of a specific essential amino

Every day, you need this much of these essential amino

14 mg/kg of histidine
19 mg/kg of isoleucine
42 mg/kg of leucine
38 mg/kg of lysine
19 mg/kg of methionine + cysteine
33 mg/kg of phenylalanine + tyrosine
20 mg/kg of threonine
5 mg/kg of tryptophan
24 mg/kg of valine

Of course, you don’t need to spend hours in your kitchen with
an eyedropper of lysine solution, carefully calibrating your

Just eat a variety of protein-rich foods and let nature
do the rest.

What does a high-protein diet look like?

People often assume that “high protein” means “low
carbohydrate”. In fact, you can eat more protein without making
any drastic changes to other things in your diet.

Many types of diets can be considered
high-protein. “High protein” is a bit of a relative
concept; there’s no clear rule.

The average protein intake for adults in the US is about 15
percent of calories coming from protein.

The Institute of Medicine suggests that up to 35 percent of
total calories is an OK proportion of protein for healthy

And most researchers would say that once you get more than 25
percent of total calories from protein, you’re in “high
protein” territory.

Here’s what high- and low-protein diets might look like for a
given meal.

2016.08-Pn-Low protein-American-Meals-1

The upper tolerable limit (UL) of something tells you how much
you can eat without having health problems.

Currently, there’s no established UL for

Does that mean you can eat as much protein as you’d like
without any negative side effects? No. It just means researchers
haven’t figured it out yet.

But we do know that eating up to 4.4 g/kg (2 g/lb) body
weight didn’t cause any short term health problems in
clinical studies.

Let’s take a deeper look: Calculating maximum protein

The Institute of Medicine suggests that high protein intake,
where about 35 percent of your calories comes from protein, is

What does that mean in grams per kilogram body weight (or g/lb
body weight)?

Say you’re 74.8 kg (165 lb) and reasonably active. You need
about 2,475 calories per day to maintain your weight.

If you get 35 percent of your total energy intake from protein,
you’d be eating about 866 calories from protein each day.

1 gram of protein has 4 calories. So 866 calories is around 217
grams of protein per day.

That’s about 1.3 grams per pound of body weight, or 2.9

Will eating a high-protein diet hurt me?

For years, people have been concerned with the safety of eating
too much protein.

Will eating too much protein explode my kidneys?

How about my liver? My left femur?

The most common health concerns of eating more protein are:

kidney damage
liver damage
heart disease

Let’s explore these.

Claim: High protein causes kidney damage.

This concern about high protein and kidneys began with a
misunderstanding of why doctors tell people with poorly functioning
kidneys (usually from pre-existing kidney disease) to a eat a
low-protein diet.

But there’s a big difference between avoiding protein because
your kidneys are already damaged and protein actively damaging
healthy kidneys.

It’s the difference between jogging with a broken leg and
jogging with a perfectly healthy leg.

Jogging with a broken leg is a bad idea. Doctors would probably
tell you not to jog if your leg is broken. But does jogging cause
legs to break? No.

That’s the same thing with protein and kidneys.

Eating more protein does increase how much your kidneys have to
work (glomerular filtration rate and creatinine clearance), just
like jogging increases how much your legs have to work.

But protein hasn’t been shown to cause kidney damage —
again, just like jogging isn’t going to suddenly snap your leg
like a twig.

High-protein diets do result in increased metabolic waste being
excreted in the urine, though, so it’s particularly important to
drink plenty of water to avoid dehydration.

Verdict: There’s no evidence that high protein diets
(2.2g/kg body weight) cause kidney damage in healthy

Claim: High protein causes liver damage.

The liver, like the kidneys, is a major processing organ. Thus,
it’s the same deal as with kidneys: People with liver damage
(such as cirrhosis) are told to eat less protein.

Yes, if you have liver damage or disease you should eat less
protein. But if your liver is healthy, then a high-protein diet
will not cause liver damage.

Verdict: There’s no evidence that high-protein diets
(2.2g/kg body weight) cause liver damage in healthy

Claim: High protein causes osteoporosis.

Eating more protein without also upping your fruit and vegetable
intake will increase the amount of calcium you’ll lose in your

That finding made some people think that eating more protein
will cause osteoporosis because you’re losing bone calcium.

But there is no evidence that high protein causes

If anything, not eating enough protein has been shown to cause
bone loss. Bones aren’t just inert sticks of minerals — a
significant proportion of bone is also protein, mostly
collagen-type proteins.

Like muscle, bone is an active tissue that is constantly being
broken down and rebuilt. And like muscle, bone needs those Lego
building blocks.

Women aged 55 to 92 who eat more protein have higher bone
density. So eating more protein improves bone density in people
most at risk of having osteoporosis.

(Eating more protein plus adding resistance training: Double win
for bone density.)

Verdict: High protein diets do not cause osteoporosis,
and actually may prevent osteoporosis.

Claim: High protein causes cancer

Unfortunately, we still don’t have conclusive human studies on
the cause of cancer and the role of protein.

There are studies that asked people how much protein they ate
over their lifetime, and then looked at how often people got
cancer. The research shows a connection between protein intake and
cancer rates.

But these studies are correlational studies and don’t prove
that protein is the cause of cancers. Plus, some researchers have
gone so far to say that studies relying on subjects to recall what
they ate are basically worthless because human memory is so

A big part of the proposed cancer and protein link comes down to
confounding factors, like:

where you get your protein from — plant or animal
how you cook your protein (i.e. carbonized
grilled meat
what types of protein you’re eating (e.g. grass-fed steak
versus a hot dog)

And so on.

In other words, we can’t say that any particular amount of
protein causes cancer.

Verdict: Limited evidence that protein causes cancer;
many other confounding factors.

Let’s take a deeper look: Protein and cancer

A study from 2014 looked at protein and cancer risk. It was
widely misinterpreted as proof that eating a lot of protein caused

First, it was actually two studies, one asking people questions
and following them for years; and one that fed mice a high-protein
diet and implanted them with cancer.

With the human study, researchers looked at people’s
self-reported protein intake and their rates of cancer over the
following 18 years.

They found that people aged 50-65 who ate diets high in animal
protein (≥20% of total calories) had a 4-fold greater risk of
dying of cancer over the next 18 years compared to people who ate a
moderate amount of protein (10-20% of total calories).

(Just so you get an idea, smoking increases your risk of cancer
by 20-fold.)

Then, it gets more interesting, because for people over 65,
eating more protein decreased cancer risk by more than half. In

Eating more protein from 50-65 years old was associated
with a higher risk of death from cancer, but over 65 years old that
association was reversed.

The second part of the study is where people really
misunderstood what the study had proven.

Researchers fed mice a high-protein diet (18% of total
calories), then implanted cancerous cells. They found that the
high-protein diet increased tumor size. This is not a surprise,
since protein increases IGF-1 (an anabolic protein) that stimulates
growth in pretty much all tissues, including cancerous tissue.

Higher protein diets stimulated cancerous growth in

So, while eating more protein might increase the size of
existing tumors (depending on what treatment someone is
undergoing), this study does not show that high-protein diets cause

Claim: High protein causes heart disease.

Eating animal-based protein daily is associated with an
increased risk of fatal coronary heart disease (70 percent for men
and 37 percent for women), whereas plant-based proteins aren’t
linked to higher rates of heart disease.

This suggests that where you get your protein from may matter
more than how much protein you eat.

However, just like cancer, the link between heart disease and
high-protein diets is from questionnaires rather than a
double-blind randomized study (the gold standard in research).

There are many confounding factors. For one, consider the type
of animal — does seafood cause the same issues as red meat, for

We don’t yet know the whole story here.

Verdict: Limited evidence that protein causes heart
disease and the source of protein is a major confounding

Let’s take a deeper look: Protein source

A new study in the Journal of American Medical Association
(JAMA) looks not only at protein intake, but where people got their
protein from.

More than 131,000 people were asked:

how much protein they ate; and
if it came from animals or plants.

This study took over 35 years to do (starting in the 1980s).

What they found:

Eating more animal protein was associated with a higher
risk of death… if you were also doing something else that was a
risk factor.

Such as:

being overweight
not exercising
drinking alcohol
history of high blood pressure
low intake of whole grains, fiber, and fruits and

Eating more plant protein was found to be associated with lower
risk of early death.

What does this mean?

You might think at first glance that you should eat less animal
protein, since this study seems to say that animal protein is bad
for you.

But there’s more to it.

If you’re doing everything else “right”, then
eating more animal protein doesn’t seem to be a

Likely, it’s not the animal protein on its own but a lot of
lifestyle things that come with eating more animal protein.

For instance, this study began in the 80s. At that time, nearly
every doctor told their patients to eat less fat and meat, and to
avoid eggs.

So if you were a somewhat health-conscious person, then you’d
likely be eating less animal protein compared to someone who was
less health-conscious (or if you went against your doctor’s
advice) — but you’d also likely be engaging in a bunch of
other health-supporting decisions and activities.

The problem with these types of studies, called correlational
studies, is that you can never be sure whether the associations are
caused by one onto the other or if they’re simply happening at
the same time.

Protein quality matters

Most people think about how much protein, but they don’t think
all that much about the quality of the protein they’re

There are huge differences in the chemical makeup of a given
protein source, and how valuable that protein is nutritionally.
The higher a protein’s quality, the more easily it can give your
body the amino acids it needs to grow, repair and maintain your

The two big factors that make a protein high or low quality


How easy is it to digest?
How much do you digest — and absorb and use?

Amino acid composition:

What amino acids is it made of?

A high-quality protein has a good ratio of essential amino
acids, and allows our body to use them effectively.

Amino acid composition is more important than digestibility.

You can have way more protein than you need, but if the protein
you’re eating is low in an important amino acid (known as the
limiting amino acid), it causes a bottleneck that stops everything
else from working (or at least slows things down).

High-quality proteins have more limiting amino acids, which
means the bottleneck is lessened and our bodies can use that
protein source better.

Let’s take a deeper look: Measuring protein’s worth

Scientists use many ways to calculate protein quality, or how
well we might digest, absorb, and use a given protein.

Here are a couple.

Protein Digestibility Corrected Amino Acid Score

PDCAAS is calculated using a ratio of limiting amino acids and a
factor of true digestibility to give you a value that lets you know
how much of a given protein is digestible.

The higher the score, the higher the quality of protein.

PDCAAS is the current gold standard for measuring protein
quality, but there are a few other protein quality scoring methods
that we cover in the Precision Nutrition Level 1 Certification

Indicator amino acid oxidation (IAAO)

When we don’t have enough of a particular indispensable amino
acid, then all the other amino acids, including that indispensable
one, will be oxidized (i.e. essentially wasted) rather than used
for stuff like repairing tissues.

It’s kind of like a team sport: You can’t play without the
goalie, so all the players sit around twiddling their thumbs, even
though they’re all great players in their own right.

But if we’re getting enough of that particular amino acid,
then we won’t see all that oxidation. We have a goalie and the
rest of the players can play.

So, you want the IAAO score to be low, indicating that all your
amino acids are doing their jobs to rebuild you.

Thus far, the IAAO method seems like a very useful way to judge
the metabolic availability of amino acids from different
protein-containing foods, and to determine total protein
requirements for all kinds of people.

New assessment techniques like IAAO are giving us a more precise
idea of protein use, which means that we may see recommendations
change in future.

Most likely, based on these recent findings, the RDA for
protein will increase — i.e. doctors may tell us to eat more

“Complete” and “incomplete” proteins

Back in the day, scientists used to talk about “complete”
and “incomplete” proteins.

If you had a plant-based diet (i.e. vegetarian or vegan), you
were told that you had to eat a mix of incomplete proteins (i.e.
protein from a variety of plants) at each meal in order to meet
your needs.

We now know this isn’t true.

As long as you eat a mix of different protein sources,
you’ll get all the amino acids you need. No need for
mealtime protein algebra to make sure you’re getting all your
amino acids.

That being said, many plant-based sources are less protein-dense
than animal sources. So if you choose not to eat animal products,
you’ll have to work a little harder to get more protein from a
wide variety of plant sources to make up the difference and meet
your protein needs.

2016.08-Protein per serving chart-1.1-01

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