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.
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:
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
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.