Carbs! Who are you?

Carbs are crucial for our well-being; indeed, apart from providing us energy, they are involved in many other physiological processes such as: synthesis of amino acids, DNA, RNA, ATP; etc.

Nutritionally carbs are classified as DIGESTIBLE and NON-DIGESTIBLE carbohydrates.

DIGESTIBLE carbs are those digested by our intestinal enzymes and then absorbed in the small intestine. Once absorbed, these carbs are transported by the blood stream to various tissues in order to be used. This group consists of monomers such as glucose, fructose and galactose (in fruit and honey); di-saccharides such as sucrose and lactose (milk); and polymers such as starch (in cereals, legumes and vegetables).

Differently, NON-DIGESTIBLE carbs cannot be degraded by our intestinal enzymes. These carbs escape the intestinal digestion in the small intestine and reach the large intestine, where they can be potentially fermented by our symbiotic microflora. NON-DIGESTIBLE carbs are commonly known as dietary fibers, which are mainly of plant origin and consist of: cellulose, hemicellulose, beta-glucans; resistant oligo-saccharides (e.g. fructans and galactans); resistant starch and lignin. Although we cannot digest and absorb them, NON-DIGESTIBLE carbs are still crucial to us since they serve as “food” for our symbiotic intestinal micro-flora, which performs essential functions (i.e. activities we cannot accomplish) for our physiology. In fact intestinal micro-flora is responsible for the regulation of the energy metabolism, the proper development of many organs (e.g. brain, immune system) and protection from intestinal pathogens.

Moreover fibers can exert other activities not related to intestinal micro-flora: for example they help to regulate the transit time, to protect from toxic xenobiotic, etc..

Ultimately we need to eat both types of carbs for our well-being.

Thank you

Ciao

Francesco

Glucose mon amour: in defence of carbs

In last decades carbs have gained a bad reputation: it seems they are the only responsible for the epidemic spread (in affluent countries) of overweight and obesity. Many types of diet recommend a very low intake of carbs, especially sucrose and those carbs derived from cereals, in order to prevent or reduce any accumulation of fat storage and diet-related diseases (diabetes, cardiovascular diseases, etc.). This is partially true, since any excess of dietary energy (in form of carbs, proteins or lipids) is stored as fat in the adipose tissue ⁽¹⁾. 

In nutrition it is defined as essential any necessary dietary compound which cannot be synthetized by our body; these compounds to fulfil our physiological requirements must be obtained from food. Glucose cannot be termed as essential since our body can produce this molecule from non-carbohydrate substrates: the process is called as gluconeogenesis and occurs in the liver, where amino acids, lactate and triacylglycerol can be converted into glucose. Gluconeogenesis is a crucial process since it allows the survival of those tissues which energetically depend only on glucose (e.g. red blood cells, brain), when glucose availability is too law. Unfortunately the rate of glucose production by gluconeogenesis is lower than the rate of glucose oxidation by tissues, therefore it is necessary to use exogenous glucose deriving from the diet in order to avoid detrimental consequences for our body. This requires that at least 20 -30% of our energy intake must come in form of carbs (mainly glucose and its polymers, such as dextrin, starch).

There are two rules to keep in mind:

1^st – no energy no life;

2^nd – no natural dietary compound can be considered as noxious for our body; its toxicity depends on the amount consumed. So don’t avoid glucose, sucrose or starch, just learn the right level you need to eat.

Ciao and take care.

 

⁽¹⁾ I’d like to highlight that the immediate decrease of weight produced by low carb diets doesn’t correspond to a real adipose tissue reduction: the loss of weight is due to a reduction of the water associated to glycogen (that is the form in which carbs are stored in our body).

How we use food to produce energy: introducing the concept of Cellular Nutrition

The human body can be seen as a biological machine and food is the fuel necessary for the functioning of this machine. Many substrates of dietary origin can be used as metabolic fuel:

·        glucose is the main form of dietary energy and derives from the digestion of carbohydrates (fructose and galactose are minor monomers obtained from carbs);

·        fatty acids, from dietary fats, are the second major source of energy;

·        amino acids, obtained from the breakdown of dietary proteins, are also an important source of energy.   

The conversion of the food into usable energy occurs inside every single cell. Indeed our body doesn’t contain a specific organ able to perform this conversion and then the distribution of the energy to various tissues. Generally any type of cells, a part from few types (e.g. red blood cells),  has specific organelles, termed as mitochondria, able to generate energy (mainly in form of ATP) from dietary compounds.

The demand for energy depends on the metabolic rate of distinct tissues and organs. For instance adipose tissue has the lowest metabolic rate, while liver, brain, heart and kidney are metabolically the most active tissues.

Tissues can use different metabolic fuels depending on the fuel availability and physiological conditions, as showed in the following table

Tissue	Metabolic fuels for distinct tissues
Brain	Glucose (almost exclusively), ketone bodies (prolonged starvation)
Muscle	Glucose, fatty acids, ketone bodies (starvation), acetate (after alcohol ingestion), triacylglycerol, branched-chain amino acids
Liver	Amino acids, fatty acids, glucose, alcohol
Kidney: ·        Cortex ·        Medulla	Glucose, fatty acids, ketone bodies Glucose
Gastrointestinal tract: ·        Small intestine ·        Large intestine	Glutamine, ketone bodies (starvation) Short chain fatty acids, glutamine, glucose
Red blood cells	Glucose
Leukocytes	Glutamine, glucose, fatty acids

 

Ultimately any single cell of our body is an independent energy factory, able to fulfil its own energy requirement using various dietary molecules.

Ciao