Friday, 10 August 2018

Feedback regulation of food intake

The physiological regulation of the food intake has two kind of feedback signals: long-term and short-term. The long-term feedback signals are derived from the adipose tissue and reflect the size of the adipose tissue stores. The short-term feedback signals originate from the gastro-intestinal tract and influence satiation and satiety. The signals are received in the hypothalamus and are integrated with emotional stimuli (mood), cognitive stimuli (thinking), hedonic stimuli (liking), influencing hunger, appetite and food seeking behavior.

On food intake, the immediate distension of the stomach (stretching) will send the feeling of fullness. The food entry on the gastro-intestinal tract will inhibit the release of the hunger hormones and stimulate the release of the satiety hormones (cholecystokinin - CCK AND glucagon-like peptide 1 -GLP1). The entry of glucose and amino-acids into the blood stream will activate the nutrient sensing cells from hypothalamus.

Long-term regulation - the leptin hormone produced by the fat tissue (the production and the blood levels of leptin are proportional to the amount of fat mass, converging the feeling of satiety, sending signals to the satiety cells in the hypothalamus. Lack of leptin due to the genetic disease will lead to extreme hunger, massive overfeeding and obesity. While the animals tends to have a relative stable body weight, the human's body fat tends to increase with age.

When we fast, we release hunger hormones, the low levels of nutrients in blood will also decrease the leptin production, triggering the hunger cells in the hypothalamus. Raising an effective hunger response and being effective at storing body fat is critical for survival.

Let's see a bit more about the feedback regulations from adipose tissue. When we have a body fat gain, the increased leptin release will stimulate the satiety cells in the hypothalamus, decreasing the food intake, decreasing the energy storage. When we lose body fat, the decrease of the leptin will trigger the hunger cells from the hypothalamus, increasing the food intake and increasing the energy storage.

The adipose tissue( fat ) has a central role in the long-term regulation of food intake. The leptin reduction during weight loss is one of the reasons of being difficult to maintain the weight loss.

The next post will be about the energy value of nutrients, maybe after i come back home. 

Wednesday, 8 August 2018

Factors determining food intake

There are few factors determining the food intake, and we should be aware of them if we want to follow a diet successfully.

1. Sensory factors - sensory properties of a meal (combination of taste, smell, sight and even sound). We eat more of what we like and less of what we do not. Chefs are experts in optimizing the sensory aspect of any food.

2. Social factors - much of what we eat is determined by our culture, and people with different background can possess different culinary customs. Social settings are also underlined, as we eat more in company of others than we eat alone (food made for social bonding as barbecue and food made to celebrate special events as birthday cake). Social factors can override physiology (thousands of calories on our Christmas dinner for example). If you try to improve dietary habits, the social settings can be an impediment towards your goal.

3. Psyhological factors - losing appetite when stressed or eating for comfort (increasing the food intake due to emotional eating is a major cause of weight gain).

4. Physiological factors - our physiological needs dictate the food choice The desire for food is driven by the evolutionary need to supply our bodies with nutrients and energy in order to survive. There are complicated feedback mechanisms (long term and short term) leading to hunger sensation an food seeking behavior when food intake and energy levels drop. On long term, the energy intake will always match perfectly the energy expediture, proving the existence of overriding physiological feedback mechanisms that resist to large fluctuations in body weight.

I will try to put all this in some coherent post about the feedback regulation of the food intake and, as an added bonus, also about feedback regulation of the adipose tissue (fat). Hope you will enjoy it.

Talk to you soon!

G.

Monday, 6 August 2018

Energy balance (food related)

As i was talking quite a lot about proteins, i will stop here. I will start a new series of articles, related to energy homeostasis and balance.

First i need to underline some definitions.

Energy balance is defined as the balance between energy intake (in) and energy expediture (out).

We have three situations:

Energy intake is bigger than the energy expediture, you are gaining weight (energy is stored as fat).
Energy intake is lower than the energy expediture, you are losing weight (fat used as energy).
Energy intake is equal to the energy expediture, you keep the same weight.

Energy intake - via macro-nutrients (carbohydrates, fat and protein) - they contain energy, used as fuel or stored as body fat.

Now i will speak about the food intake and some specific qualities.

Satiety - is the feeling of satisfaction that occurs after a meal. This will prevent you from eating until next meal.
Satiation - feeling of satisfaction and fullness that occurs during a meal. This will make you to stop eating.
Hunger - uncomfortable sensation caused by lack of food.
Appetite - integrated response to the sight, smell, thought or taste that triggers eating.

Now, understanding these four notions is the key to any successful diet. 

While the satiety determines how much time passes between meals, the satiation determines how much food is consumed during a meal. Foods promoting satiation are very bulky, high water content and fiber, and they got strong sensory attributes. Veggies for example, eating them causes satiation. Thinking about texture, a watermelon is more satiating than watermelon juice. Calories ingested quickly are not properly sensed (think about fizzy drinks). Prolonged exposure time to the food (chewing) causes people to quit sooner and consume less energy overall.

Energy from fluids is less satiating than the energy from solids. That's why the consumption of sugary beverages may lead to over-eating, increasing the occurrence of obesity in many occasions. This is not accepted by the beverage industry and there is misleading advertising and powerful lobby against it. But, if we use our common sense, we can realize that it is true.

Enough for today, I will post soon about the factors determining the food intake (physiological, sensory, psychological and social, to name a few).

See you!
G.

Sunday, 22 July 2018

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.


Friday, 20 July 2018

Protein turnover and nitrogen balance

Today i will speak a bit about protein synthesis and protein degradation. The protein balance, also known as nitrogen balance, is the balance between protein input and protein output. The Protein turnover consist mainly in changing the ingested proteins into aminoacids, and then using the aminoacids resulted to synthesize the proteins needed in our body. For some proteins the turnover is fast (less than 2 hours), for others can be slow (up to 12 months - structural proteins). But on average in 12 months our body is completely renewed.

When we talk about protein balance, we are thinking at the input and output in terms of carbon = energy and urea = nitrogen. Because most of the nitrogen in the body is on protein form, measuring the nitrogen intake and excretion results in finding the nitrogen balance, which is more or less equal with the protein balance.

In normal conditions the protein input is equal with the protein output. In some cases the input is bigger than the output, we are talking about a positive balance (this will happen in pregnancy, growing-up children, gaining weight through bodybuilding or in recovering patients). Negative balance (when the input is lower than the output) happen in case of illness, losing weight, low protein intake, burns or heavy trauma.

On average we will have 80 grams of dietary protein and 70 grams of residual protein, 150 grams of protein in total. The output will be 150 grams also, mainly urea and undigested proteins via stools with the carbon used for energy.

The aminoacid will divide in urea (the nitrogen part) and carbon dioxide CO2 and water (from the carbon part). Some aminoacids carbon part can be converted into glucose (gluconeogenic aminoacids). If they cannot be converted, they are called ketogenic aminoacids. The gluconeogenesis process will start during prolonged fasting to maintain the blood sugar levels. But except for this case, most people will increase the protein degradation if they increase the protein intake.

Saturday, 14 July 2018

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.

Hope

She was leaning forward, ready for a kiss. But he put a finger on her lips, whispering:
"Not now. Find me later"

Opening her eyes, Maria realized that she is still in her home, on her sofa. And then, her eyes could see the address card laying in the middle of the bowl, on her coffee table. It was not just a dream after all.

It was a black, metallic, little square of paper, with golden letters. Queen Industries, followed by an address." It was not a dream after all. Or i just fall asleep and wake up in the middle of a full Marvel nightmare movie." she was thinking.

With a quick move, she took the card and throw it into the recycle bin. All was good again.