Energy expediture and its role in weight gain and lose

We use our net energy for maintenance (average daily expediture is 2000 kcal for female, 2500 kcal for male), for physical activity (exercising) and for growth. Our daily energy expediture can be higher or lower, depending on body size, illness or physical activity. The maintenance part is essential for our survival (things such as heart beat, brain function, respiration).

Now i will introduce some new terms. Basal maintenance in fasting state is called Basal Metabolic Rate (BMR). To this we will add the energy cost of digestion and absorption (dietary induced thermogenesis - approx. 10% of the caloric value of the meal). BMR covers 60-70% of the daily energy expediture and it is different between individuals, depending of the lean body mass (body mass remaining after we subtract the fat). Tall people with lot of muscle will have a much higher BMR than short fat people.

Physical activity is measured by PAL (Physical Activity Level) and is defined by the daily amount of physical activity of a person. This vary from 1.4 for sedentary people to 2.0 for athletes, with 1.6-1.7 being the average Joe. Can be measured though the oxygen consumption (indirect calorimetry).

As for growth, we will think at the net energy required to make extra tissue. It is close to zero for weight stable adults, relevant for children and pregnant women.

We store energy as fat, a dense and easy to use form of energy. The average amount of fat stored by a normal individual is 90.000 kcal (enough to support us for 30 days of fasting, but this can last for months if you are obese). Average amount of proteins stored is 36000 kcal, but you can use only 12000 kcal in case of emergency, before you start to compromise some of the normal body functions. Average amount of carbohydrates stored is 1400 kcal in the muscle and 350 kcal in the liver as glycogen, and it is used to maintain the blood glucose level in between meals.

When the energy intake is exceeding the energy expediture, the excess is stored as fat and we will experience weight gain. After a certain margin (let's say 600 kcal), the body weight tends to level off after a while, even if initially will go up, as the energy expediture also increase with the weight gain, until a new equilibrium is reached at a higher body weight. Why, you will ask? Because the BMR will increase as the body weight increase, even if the BMR is mainly determined by the lean body mass. The energy cost of the physical activity will be higher with greater body-weight (you need more energy to use your body as your overall body mass increase.

The opposite happens if we lose weight. Weight loss is rapid at first, but progressively slows down as the energy deficit decrease. Losing weight, the energy expediture decrease as well as BMR and the energy required for physical activity decrease, until a new equilibrium point is reached. This is the reason why every diet will work well at first, but lose efficiency over time.

Next post will be about weight management and obesity.

Energy value of nutrients

Today we will talk about the energy value, Atwater factors, metabolizable energy and kilocalories.

Our energy value come 30-70% from carbs, 15-50% from fats and 10-25% from proteins. The Adwater factors are:

-gross energy - all the energy present in the food products (not all is available)
-digestible energy - amount of energy absorbed, dependent of the digestibility of the food (carbs 98%, fats 95%, proteins 92%)
-metabolizable energy - what is left after accounting the energy in feces and urine.

So, the gross energy is made by the digestible energy and the one not available. The digestible energy is made by the metabolizable energy and the energy eliminated through feces and urine. The energy eliminated is mostly made from proteins (30% of it as urea). The calories we see on the food package are in fact equal with the metabolizable energy.

In terms of kilo-calories (kcal), we have the carbohydrates and proteins with 4 kcal, fats with 9 kcal and alcohol with 7 kcal. In terms of dietary fiber, the insoluble one is subtracted from the carbs content, and the soluble ones have 4 kcal per gram. According to the EU rules, all the fiber is considered to have 2 kcal per gram.

The Atwater factor is an average, but in real life the digestibility can be different. For example, from the thermic effect of food point of view (dietary induced thermogenesis), the transient increase in energy expediture following meal consumption, caused by digestion, absorption and processing of the nutrients, it is higher for proteins than for carbohydrates and fats. Also, proteins, fats and carbs have different effects on hunger and satiety.

In conclusion, the traditional view that all energy is equal regardless of the source (a calorie is a calorie) is overly simplistic and often wrong in real life.

Next post: energy expediture.

Protein quality and recommendations

For optimal synthesis of body protein, all the aminoacids need to be present in adequate quantities and proper proportions. Any essential aminoacid deficit will drastically limit the synthesis of much needed protein.

You need to learn about the concept of limiting protein. The limiting protein is the least abundant aminoacid in a dietary protein source (for example for wheat the limiting protein is the lysine). By combining different dietary protein sources you will provide with a wide array of aminoacids.

Protein quality has two variables. First is the digestibility (what percent of the dietary protein is absorbed into the body), second being the aminoacids composition (the higher the similarity of aminoacids composition and the average body protein, the higher is the quality, so, obviously, animal proteins are better than plant proteins, unless you combine various sources). A meal or a diet should have a mixture of different  proteins. A mixture of plant-based proteins will have a more favorable aminoacids composition than one individual plant. This is called protein complementation - combining more proteins to achieve higher protein quality (grains are low in lysine, and beans are low in methionine, but together they are well balanced).

Methods to measure protein quality:

1. Biological value (BV) - measure of the protein percentage absorbed from a food to be incorporated into the body.

2. Protein efficiency ratio (PER) - weight gain divided by its intake of a particular protein during test period. PER was the official method before getting replaced by PDCAAS (protein digestibility corected aminoacid score). AAS (aminoacid score) is calculated for any particular protein comparing the level of limitating aminoacid in the protein towards the level of the same aminoacid in a reference protein. PDCAAS for milk is 1, for isolated soy protein is 1, for wheat is 0.4, for beans is 0.6-0.7, but wheat combined with beans is almost 1. PDCAAS is easy to calculate , based on the human aminoacids requirements.

DIAAS (digestible indispensable aminoacid score) - the diference is that, while for PDCAAS indigestability of a particular protein is measured in stool, for DIAAS is measured in terminal ileum, being more accurate.

The recommended protein intake is 0.8 grams per kilogram weight (56grams for a 70kg adult). Most people have more than RDA (required daily ammount), as protein is 10-25% of our total energy intake. You will have above 20% if you eat mostly meat, eggs and dairy. Endurance and strenght athletes eat 1.2-1.7 grams per kilogram (and many do not know that you can achieve this through diet alone, without any supplementation). According to the Journal Of Sport Sciences, it is ideal to consume them as soon after exercise, for them to be optimally used.

Beware: even if it is unproven, there are some potential health effects of protein that are promoted by media.

- High protein intake to be avoided by patients with kidney disease.
-No conclusive evidence to link proteins to cardiovascular diseases, cancer or osteoporosis.
-No conclusive evidence that there is a relation between protein intake, energy intake and body-weight.
-Between animal and plant-based proteins, the animal food is bad because of the package (more fats, salt and carbs), not because the proteins from the aminal sources are bad.

Next posts will be about energy requirements and energy balance. Have a wonderful day!
G.

Protein functions

The proteins are used for a multitude of functions in the cells and in the tissues. The function of a protein is determined by two factors: the aminoacids sequence and the folding of the polypeptide chain. Thinking about this, a persistent faulty incorporation of one incorrect aminoacid in the polypeptide chain can cause a severe disruption of the protein function, being the basis of many genetic diseases.

The main protein functions in our body are:

1. Building material. They got an important structural role outside and inside the cell. The main structural protein is collagen, which is also the most abundant, being found in skin, tendons, cartilage, bone, connective tissue and giving structure and strength to tissues and cell. Defects in collagen synthesis can result in brittle bones (osteogenesis imperfecta). 

2. Enzymes. Are defined as proteins that speed up a biochemical reaction, having a catalyst function, by lowering the activation energy barrier needed to be overcome for a reaction to happen. Every cell has more than one thousand enzymes responsible for different reactions (like those required to generate energy by breaking down glucose or fatty acids).

3. Transporters (totally unrelated to Jason Statham movie). They offer assistance with the transport of different molecules across the cell membrane (in and out).

4. Hormones. They are messengers circulating via blood stream, released from a specific tissue into the blood to signal something to distant tissues ( like the insulin released by pancreas to reach muscle and fat tissue to promote glucose uptake). Chemically speaking, the hormones are either polypeptides or steroids.

5. Antibodies. They are involved in defending the body against pathogens such are viruses and bacteria, and are called immunoglobulins, secreted by plasma cells, with the role of creating an immune system.

6. Regulation of fluid balance. They are taking care of the water being appropriately distributed across the blood stream (intravascular), in the space between the cells (intercellular) and inside the cells (intracellular).

Next post will be about protein turnover and nitrogen balance, and maybe some more extra bits. Have a nice day. See you soon.

Protein absorption and digestion

Let's talk about the digestion of protein, through polypeptides, all the way to the final product, the aminoacids.

The digestion of the protein starts in the stomach, where the enzyme called pepsin will break the polypeptides into smaller parts. The highly acid medium will help this to happen. The digestion continue in the duodenum and upper small intestine, where the pancreas will secrete another enzyme called chymotripsin, with the role of breaking the small polypeptides into even smaller polypeptides. The final work is done in the lower small intestine, where carboxypeptidase and aminopeptidase enzymes will break everything into aminoacids, and they will be absorbed into the blood stream. About 5% of the proteins will leave the body undigested, through feces.

The single molecules of aminoacids are taken up into the blood stream and distributed across the human body, used to synthesize the so much needed proteins (like albumin in liver or muscle proteins in muscle) and they can have extracellular functions, such as hormones and cell adhesion, or intracellular, such as generating fuel, cell structure, signal transduction. You can find more than 100.000 proteins in our body.

The protein digestion starts in the stomach, when the acid environment causes proteins to unfold, allowing pepsin to access the dietary protein easier. The pepsin enzyme is produced by the Chief cells lining the stomach, and it is present as an inactive pro-enzyme called pepsinogen, being activated by the high acidity. The pepsin will cleave the peptide bonds, creating small polypeptide from the protein. The process is further going into the small intestine (upstream), with the polypeptides being cleaved into even smaller polypeptides under the influence of trying and chymotripsin (which are also created by pancreas as inactive pro-enzymes, being activated when they reach the intestine). In the downstream on the small intestine, the polypeptides are finally transformed into individual aminoacids, under the action of aminopepsidase and carboxypepsidase (both of them produced by the intestinal cells). Those last mentioned enzymes will remove single aminoacids from each end of the peptide. The single aminoacids are taken to the liver, after they were being absorbed via portal circulation, and to the rest of the body, used as building block for the synthesis of the body proteins. In the liver, they are mainly used to synthesize the main serum protein called albumin.

In the next post I will talk about the protein functions (enzymes, structural, hormones, transporter, antibodies and so on).

Introduction to proteins as macronutrient

A short introduction about proteins, composition chemistry and protein content of different foods.

All the proteins are polypeptides, composed of different amounts of amino-acids. We have 20 different amino-acids in their composition, of which 9 are essential and they need to be provided in the diet. The other 11 non-essential ones can be synthesized by our body using the essential ones. The amino-acids are linked through peptide bonds. If there have two, they are called dipeptide, if they have three, tripeptide and so on. The complex proteins have hundred, even thousands of peptide bonds. In each food we have different proteins in different quantities. The amino-acid has a acid group (carboxyl) and an amino group. Depending on the structure, they can be hydrophilic (water loving) or hydrophobic (fat loving).

Let's see some foods and their protein content:

Peanuts 25.5%
Cheese 24.5%
Pork chops 20.4%
Chicken breast 22.8%
Steak 23.8%
Salmon 20.2%
Wheat 12.4%
Bacon 15.2%
Cod 16.4 %
Eggs 12.5%
Milk 3.5%

Protein content of a real food never exceeds 25-30%. There are protein powders used for bodybuilding, containing protein up to 90%, but after they are diluted with milk, water or juice, they will have on average 20% protein content.

Adult vegans can get their protein from soy, nuts, beans and grains, but young children need dairies at least,and maybe eggs,  because while the vegan diet is possible, it is not recommended for children, as very often the parents need solid knowledge related to the mater.

Next post will be about the protein absorption and digestion. See you soon.