Protein breakdown begins in the stomach, where it is aided by hydrochloric acid and the enzyme pepsin. The product polypeptides move from the stomach into the proximal small intestine once the initial protein denaturing and peptide cleaving is complete. Almost all of the digestion of proteins and absorption of amino acids occurs in the proximal small intestine (the duodenum). A very small amount gets excreted in the feces. Here, there are even more digestive enzymes present to break down the remaining polypeptides into their amino acids, along with some trace amounts of di- and tri-peptides.
For example, someone may eat 40 grams of protein all at once. If we only assume that 30 grams are absorbed at a time, then the extra 10 grams will be excreted in the feces. This, however, is just plain false. The gut's ability to absorb protein is nearly complete, with only a small amount not being absorbed. So if you can't even absorb all the protein you're eating, how are you supposed to store the extra as body fat? There is a difference between utilization and absorption that most people don't realize.
Liver, the Primary Site for Amino Acid Metabolism
The amino acids released from the small intestine are going to the liver. The liver takes in more than half of all of the amino acids that are consumed (in the form of proteins). The liver regulates the metabolism of amino acids that are absorbed by the body, depending on the body's current needs. It is here the initial claim comes into play.
George Bray and colleagues attempted to find out in 2012 if the amount of protein in a person's diet affected their body composition, how much weight they gained, and/or how much energy they expended. The subjects were randomly put into one of three groups based on the amount of protein in their diet: low protein (5%), normal protein (15%), or high protein (25%). The subjects were randomized and then admitted to a metabolic ward, where they were fed diets that were 1,000 calories more than their normal maintenance needs every day for 8 weeks. The average intake of protein was approximately 47 grams per day for the low protein group, 140 grams per day for the normal protein group, and 230 grams per day for the high protein group. The amount of carbohydrate was the same for all groups, while the amount of fat differed, with the high protein group having 33% fat, the normal protein group having 44% fat, and the low protein group having 52% fat. The subjects' body composition was measured every two weeks using dual x-ray absorptiometry (DEXA) during the 8-week period of overeating.
Results
Despite increasing their intake of calories, all subjects gained weight with similar increases in body fat between the three groups. Although the higher protein groups gained slightly less body fat than the lower protein group, this difference was not significant. The group eating the low-protein diet gained the slightest amount of weight in comparison to the other groups, with the normal and high-protein group gaining about twice as much weight.
However, the additional body weight gain in the normal and high protein groups was shown to be due to an increase in lean body mass and not body fat. To quote the conclusions of the authors:
” Body fat increased due to the number of calories consumed. Protein had an effect on lean body mass, but not on the amount of fat in the body.
We can't be certain of the exact lean mass that was gained, but we can say definitively that the extra protein was not mostly used for storing fat. I suspect that the protein that was not used for synthetic purposes was mostly converted to glucose and stored as glycogen with the water weight.
Either way, it wasn’t body fat.
Regroup
Before we go any further, let's take a moment for this to sink in. The subjects in this study had to eat 1,000 more calories than they needed to maintain their weight for 8 weeks. Even though this was a difficult task, the study showed that the protein contributed to increasing lean body mass, rather than body fat. I find it hard to argue that the people in the normal and high protein groups did not meet the requirements for energy, glucose, and protein, given that the initial claim is that any excess amino acids will be converted to fatty acids and stored as body fat. They outdid the lower protein group by a long shot, but still didn't pack on extra body fat. This is in stark contrast to what is thought.
The study shows that the number is higher than three times the current RDA. This means that either way, the number requires a similar overfeeding protocol drawn out over a longer period. Whether you're trying to lose or gain weight, it's unlikely that you'll be able to achieve your goal by consuming large amounts of protein and calories. The most someone could expect to gain from taking supplements is probably not much, and is also individualized based on other things like genetics, lifestyle, and if the person is an athlete.
We do not have the answers to these questions at this time.
Can Protein Turn Into Fat?
Short answer: yes, if you eat enough of it. But it’s not easy.
You gain weight when you consume more calories than your body uses.
One gram of fat contains nine calories. This macronutrient is easy to gain weight with, and harder to get rid of excess fat. Although fat contains more calories per gram than carbohydrates and protein, it contains less than half the calories of fat.
If you want to gain weight, eating too much bread is a great way to do it. However, your body finds it more difficult to store excess protein as fat.
Does Protein Make You Fat?
If your body doesn't need the extra glucose, it will be turned into fat. In other words, protein is not typically converted to glucose by the body because carbohydrates and fats are seen as more efficient sources of calories.
If Not Energy, What Do You Need Protein For?
Proteins are large, complex molecules that your body needs for building muscle, enzymes, and other structures that have a specific function.
Your stomach acid breaks down proteins into either amino acids or peptides, which are then further broken down in your intestines and absorbed into your bloodstream. Your body then uses the amino acids to create the proteins it needs.
How Does Eating More Protein Affect Body Weight?
Doing resistance training and eating more protein can help athletes avoid gaining fat weight, even if they consume more calories overall.
None of the resistance-trained men in the study gained weight during the 8 weeks, even though they were eating more than 5 times the recommended amount of protein. In female athletes, there is no weight gain or change in body composition.
You could end up gaining fat. If you don't exercise and you eat too much protein, you might get fat. The extra amino acids have to go somewhere.
What Is The Immediate Fate Of Excess Dietary Protein In The Body?
Protein is broken down into amino acids in your stomach and intestines. Blood carries these amino acids to the liver and the rest of the body. In the body, they are mostly turned into proteins.
But your body can’t store amino acids. If you eat more than the amount of protein needed to build functional proteins, the extra protein will be converted into glucose and stored as glycogen or used for energy.
Glucose can be converted into triglycerides and stored as fat. Some amino acids can be turned into ketones, which is an alternative energy source to glucose.
So, amino acids from excess dietary protein can get turned into either:
- Urea, which comes out in your pee.
- Glucose (which is burned for energy, stored as glycogen).
- Fat (excess glucose is turned into triglycerides and stored as fat).
- Ketones (an alternative energy source) from ketogenic amino acids.
- Energy is made directly from amino acids.
Your body only uses protein for energy as a last resort when there are not enough carbs or fats available.
Conversion to Glucose: The Last Resort
Very little glucose comes from amino acids. Eating four eggs resulted in the production of 50 grams of glucose over the course of eight hours, with only 8% coming from the amino acids.
After the person used all the amino acids they needed for protein synthesis, they burned most of the excess amino acids as energy directly.
The study used normal amounts of protein. A diet high in protein is different. If you're eating more protein than you need, your body will convert it to energy. Each gram of protein provides your body with about four calories of energy. The energy will be stored as fat if it is not needed right away.
Does Protein Make You Gain Weight?
Generally, consuming more protein leads to feelings of fullness, which can then result in weight and fat loss.
The amount of food you consume and the amount of physical activity you do determines how many calories you burn. Plus, many high-protein foods don’t only contain protein.
High-Protein Foods Contain Carbs And Fat
Additionally, if you're only eating protein and not balancing it with other nutrients, you're likely not getting all the nutrients your body needs. It is easy to gain weight by eating too much protein.
This means that if you eat more protein, you will generally eat fewer calories because it is more filling than fat or carbohydrates. Proteins take longer to digest than other nutrients, so you'll feel fuller after a meal that is rich in protein.
It can be tough to put on weight by eating more protein, but it's not out of the realm of possibility. At the end of the day, make sure you have burned more calories than you have eaten.
Does Excess Protein Turn Into Fat Or Muscle?
Gaining body weight doesn’t necessarily mean gaining body fat. If you're working out and eating more protein, you may see an increase on the scale even if you're losing fat. That's because muscle is more dense than fat.
Studies generally don't show that eating a high-protein diet leads to increased body fat. However, some studies suggest that it can lead to weight gain – but not necessarily bigger waist size.
So rather than gaining fat around your belly, you may gain muscle which would bulk you up.
Risks Of Consuming Too Much Protein
Most people eat much more protein than they need. The risks of eating too much protein are mostly due to animal sources, not plants.
Shorter Lifespan
Proteins should not be consumed in large quantities as this increases the risk of all-cause death.
A lower protein diet may be associated with a longer life span. Studies have found that one amino acid, which is particularly high in animal-based sources of protein, is associated with how long you live: methionine.
A plant-based diet can potentially extend your lifespan by restricting methionine in the diet.
Heart Disease
Eating too much red meat or dairy products can increase your risk of developing heart disease.
However, this probably isn’t referring to the protein itself. Saturated fats are found in meat and dairy products. Replacing meat with plant-based sources of protein can improve heart health.
Constipation
A diet low in fiber content is associated with an increased likelihood of digestive disorders, constipation in particular. High-protein sources of animal origin generally contain little fiber, which is essential for keeping the digestive system functioning properly.
