Nutritional Functions and Health Effects of Consuming Excess Refined Sugar, Salt and Unhealthy Fats

Many of the health problems today are linked to poor eating habits (Figure 1).

Many people eat too much saturated fat, added salt, and added sugars. Reducing their intake can help manage weight and reduce the risk of NCDs such as heart disease, stroke, type 2 diabetes, obesity, and metabolic syndrome.

Figure 1. The relationship between factors that influence obesity and non-communicable diseases (NCDs). Source: Garnett, T., & Finch, J. (2018).

Note that all images from this article can also be found in the Downloads section, where you can zoom in for better visibility.

The following figure shows data of the Spanish population as an example of overconsumption of added sugars, salt, and fat; and the derived worldwide prevalence of diabetes in 2019 and the one expected in 2045. The trend of overconsumption of these foods in Spain is similar to that which occurs globally.

Figure 2. Overconsumption of added sugars, salt and fat in the Spanish population and the World Health Organization (WHO) recommendations.

Nutritional Functions of Sugar, Salt, and Fat

Sugar

Glucose naturally present in foods and generated from the digestion of carbohydrates (disaccharides and polysaccharides) is one of the main energetic substrates for the body and brain. When it is not used, glucose is stored as glycogen in the liver and in the muscles; and if the body is lacking energy, the glucose is released into the bloodstream to be delivered and metabolized into the brain, kidney, muscle cells, and adipocytes (i.e. cells that compose the adipose tissue, specialized in storing energy as fat).

Salt

Common salt is the main source of sodium in our diet. Sodium is the principal cation in extracellular fluid in the body and is an essential nutrient necessary for maintenance of plasma volume, acid–base balance, the transmission of nerve impulses, and normal cell function. In healthy individuals, nearly 100% of ingested sodium is absorbed during digestion, and urinary excretion is the primary mechanism for maintaining sodium balance.

Fat

The human body (brain, liver, and adipose tissue) synthesizes saturated fatty acids (SFA) and their physiological functions differ according to their type. They are a great source of energy and have functional roles in cell membranes.

Part of the mono-unsaturated fatty acids (MUFAs) is synthesized by the body, and the other part is provided by the diet. They also constitute cell membranes and are of importance for enzyme, transporter and receptor activities.

Poly-unsaturated fatty acids (PUFA) play a major role in cell walls, as they insure cell communication and hormone production. This family includes essential fatty acids, linoleic acid (LA, C18:2 n-6 (omega-6)) and alpha linolenic acids (ALA, C18:3 n-3 (omega-3)), which cannot be synthesized by the body.

Fat is also necessary to facilitate the absorption of fat-soluble vitamins such as vitamin A, D, E and K.

Harmful Health Effects of Overconsumption of Sugar, Salt, and Fat

Health Problems Associated With Free Sugar Overconsumption

Free sugars refer to monosaccharides (such as glucose, fructose) and disaccharides (such as sucrose) added to foods and drinks by the manufacturer, cook, or consumer, and sugars naturally present in honey, syrups, fruit juices and fruit juice concentrates.

There is increasing concern that intake of free sugars increases overall energy intake and may reduce the intake of foods containing more nutritionally adequate calories, leading to an unhealthy diet, weight gain and increased risk of NCDs.

Many negative health effects are related to excessive sugar consumption and are shown in the attachment “Excessive consumption of added sugars can lead to serious illness” which can be found in the Downloads section below.

Consequently, since 2015, WHO recommends reducing the intake of free sugars to less than 10% of total energy intake (50 g/day) and a further reduction of the intake of free sugars to below 5% (25 g/day) of total energy intake is recommended for further health benefits.

Harmful Effects of Salt Overconsumption

Increased sodium consumption is associated with increased blood pressure, all-cause mortality, cardiovascular disease, stroke, and coronary heart disease.

Besides increasing blood pressure, recent data suggest that high dietary sodium can cause damage in different organs, including systemic vascular dysfunction, arterial stiffening, altered renal function, left ventricular hypertrophy, skin sodium deposition, cerebral circulatory dysfunction, alterations in sympathetic outflow, and potentially changes in bone content.

Therefore, WHO recommends a reduction in sodium intake to < 2 g/day sodium (5 g/day salt) in adults.

Fat Overconsumption and Its Consequences on Human Health

Excessive dietary intake of saturated and trans fats strongly influences the risk of cardiovascular diseases such as coronary heart disease and stroke, through effects on blood lipids, thrombosis, blood pressure, arterial (endothelial) function and inflammation.

However, the qualitative composition of fats in the diet has a significant role to play in modifying this risk. According to WHO, to avoid unhealthy weight gain, total fat should not exceed 30% of total energy intake (67 g of fat/day).

Intake of saturated fats should be less than 10% of total energy intake, and intake of trans-fats less than 1% of total energy intake, with a shift in fat consumption away from saturated fats and trans-fats to unsaturated fats, and towards the goal of eliminating industrially-produced trans-fats.

In the Downloads section below, you will find a chart proposed by the Harvard T.H. Chan School of Public Health that shows the beneficial and harmful fats and their food sources to be included or excluded in a healthy diet.

Authors: Dr. Dolores del Castillo and Dr. Amaia Iriondo-DeHond