Cholesterol: Killing me softly with its fat

Cholesterol has got a bad reputation since its high levels have been linked to the onset of cardiovascular diseases.

Anyway cholesterol is crucial for us. In fact it is an essential structural component of the cell membranes (of any single cell of our body) and is a precursor for the synthesis of bile acids, steroid hormones, and vitamin D. On the other side, high levels of “bad” cholesterol (the one associated with LDL) could be detrimental to us, since they could be responsible for atherosclerosis (causing stroke or heart attack) or deregulation of metabolic functions (leading to diabetes).

How can we reduce (or prevent) the abnormal accumulation of cholesterol?

We need to keep in mind that our body has been programmed to minimize the loss of cholesterol, and the only mechanism we possess for its reduction is through the intestinal secretion of bile acids. Moreover we need to consider that cholesterol can either have a dietary origin (exogenous cholesterol) or can be synthesized by our body (endogenous cholesterol). Therefore to reduce its amount we need to adopt two complementary approaches: reduction of dietary cholesterol uptake and decrease of production of endogenous cholesterol.

Cholesterol is essentially of animal origin, therefore is necessary to reduce the amount of food of animal origin. But this is not enough. Even an excessive amount of carbohydrates (these are generally present in plant origin foods) can increase the endogenous production of cholesterol.

In summary if you have high accumulation of cholesterol you need to eat less and reduce both carb-rich foods and animal fats. If you do some physical exercises is even better.

Thank you.

Take care

Ciao

The good, the bad and the ugly

What kind of carbs should I eat?

 Epidemiological studies suggest that excessive and chronic postprandial glycaemia may be related to the onset of food-related diseases (e.g. diabetes, cardiovascular diseases).   The glycaemia (the blood glucose concentration) depends on:

·         the rate of intestinal carbohydrate absorption,

·         glucose uptake by different tissues (liver, muscles, brain, blood cells, etc.);

·         insulin⁽¹⁾ secretion and the sensitivity of the tissues (muscle and adipose tissues) to insulin.

It has been hypothesized that a stable blood glucose level could help to reduce the risk of developing diabetes and cardiovascular diseases; this means we need to avoid an excessive rise of glycaemia and insulin secretion.  To maintain stable the glycaemia it is necessary to control the type and the amount of carbs we eat.

We should  prefer those carbs which produce a low blood glucose response. A simply way to discriminate amongst  different types of carbs (good, bad and ugly) is the concept of glycaemic index, which measures how quickly blood sugar increases after a meal. We should eat mainly carbs with low glycaemic index, which are those present in fruit and vegetables, legumes and whole grains. We should reduce the amount of refined carbs deriving from white breads, pasta, pizza, biscuits, cakes; we should avoid soft drinks (full of sucrose) and product containing fructose or glucose syrup (e.g. candies). Another factor influencing the glycaemic response is the amount of carbs we consume each meal. Regardless the glycaemic index, exceeding the amount of carbs required will produce an excessive rise of glycaemia and insulin secretion.

In the end, we can summarize:

·         eat less carbs (I’m pretty sure you eat more than what you need);

·         prefer carbs from fresh fruit and vegetables, legumes and whole grains;

·         minimize the consumption of refined carbs

Ciao and take care.

Francesco

 

(1)    Insulin is the hormone secreted by pancreas and is responsible for stimulating the uptake of glucose by peripheral tissues (adipocytes and muscles) and liver.

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

Why do we eat?

What is the purpose of eating?

We could answer this question  in many ways: eating fulfills our nutritional needs, but it is also a pleasure able to satisfy our social, cultural, emotional and psychological needs.

From a nutritional perspective the ultimate purpose of eating is to provide energy and essential compounds (i.e. compounds that we cannot produce and we need to acquire from the food) for the functioning of our body.

We have to consider our body as a biological machine which requires: 

•   continuous supply of energy (in forms of carbohydrates, fats and proteins);

• compounds necessary to synthesize structures vital for life (e.g. essential amino acids for proteins, fatty acids for cell membranes and hormones, etc.) and to sustain our physiology (e.g. vitamins, minerals).

Food is the only source of energy we have. Our body is designed to convert the chemical energy of foods into usable energy to performed pivotal functions, such as muscle contraction, synthesis of macromolecules, etc..

The energy provided by food can only be transformed and used at cellular level. In order to do so, food has to be processed by our body, that means: 

1. digestion in its monomeric components (e.g. carbohydrates broken down into glucose, proteins in to amino acids, lipids into fatty acids), 
2. absorption of monomers by the intestinal tract, 
3. and delivery of monomers by the blood vessels to any single cell of the body.

Food monomers can be used as fuel to generate energy only when they are inside cells; moreover cells of different tissues and organs have distinct fuel requirements. We can call this process as CELLULAR NUTRITION. 

We will talk about that next time.

Ciao