Does chronic overnutrition play a role in metabolic inflammation?
We have been looking at metabolic inflammation and its role in the development of obesity, diabetes, and other chronic diseases. Does overnutrition contribute to metabolic inflammation? How?
Background on Overnutrition
It is estimated that by 2020[b1] , two-thirds of the global burden of disease will be due to chronic non-communicable diseases, most of which are associated with an unhealthy diet. While hunger is a tremendous global health concern that cannot be minimized, overnutrition should similarly be given concentrated attention. Malnutrition affects up to 1 billion people and doesn’t just affect those who are thin due to food shortages; people who are overweight could also be malnourished.
The “double burden of malnutrition” is a term coined by the World Health Organization (WHO) to describe a situation which is characterized by “the coexistence of undernutrition along with overweight and obesity, or diet-related non-communicable diseases, within individuals, households, and populations, and across the life course. Globally, the problem is not the availability of food resources but the allocation and consumption of food.
Overnutrition is defined as the overconsumption of nutrients and food to the point at which health is adversely affected. Overnutrition can develop into obesity which increases the risk of serious health conditions including cardiovascular disease, hypertension, cancer, and type-2 diabetes.
Until recently, overnutrition had been viewed as a problem that only affected developed nations. However, this has been reviewed to affect most populations. The prevalence of obesity is increasing in developing countries with the introduction of fast food and refined sugars.
While once considered the disease of the rich, low-income groups in richer countries are also being affected by this condition.
Inflammation is a biological response launched by the immune system against dangerous assaults which threaten the integrity and normal physiology of an organism. Chronic nutrient overload causes an increase in fat tissue (adipose) irregularities in that, if adipose tissue expandability is low, there will be an increased presence of thickened tissue. This would lead to a proinflammatory state that can trigger insulin resistance, release of macrophage chemoattractant proteins, and in chronic inflammation, even the death of the thickened adipose tissue itself. This creates cyclic action that extends the insulin resistance to all adipose tissue.
An important characteristic of overnutrition-induced diseases is chronic low-grade inflammation caused by nutritional excess. Overnutrition-induced inflammation is thought to occur in the brain and thus plays an extensive and steering role in overnutrition-induced diseases.
The metabolic syndrome is a constellation of metabolic risk factors including high cholesterol, elevated blood pressure, insulin resistance and elevated serum glucose, a pro-inflammatory state, and a prothrombotic state.
Most persons with metabolic syndrome are obese and usually have abdominal obesity. Generally, obesity is a reflection of overnutrition. A current view is that when adipose tissue fails to store all excess nutrients as triglycerides, lipids (fats) begin to accumulate in various tissues (e.g., muscle, liver, pancreas, and heart). The foundation of the metabolic syndrome thus appears to be overnutrition – more nutrient intake than can be safely disposed by lipid oxidation.
When obesity is present, adipose tissue becomes inflamed. This inflammation may result in a pro-inflammatory state which could contribute to both cardiovascular disease and diabetes.
Most evidence supports the concept that fatty acids represent the final common pathway to tissue nutrient overload. Less attention has been given to the possible negative effects of excessive intake of carbohydrates.
Chronic overstimulation of insulin secretion induced by dietary carbohydrates could have the following adverse effects:
Furthermore, high-carbohydrate intakes can prompt the formation of fatty acids in the liver by way of lipogenesis; fatty acids produced in this way can feed into the final common pathway of ectopic lipid accumulation. There is thus need to look further into the role of carbohydrate overnutrition in the development of the metabolic syndrome.
Obesity in the United States has reached startling heights. The National Center for Health Statistics at the Centers for Disease Control and Prevention (CDC) estimated that in 2015-2016, the prevalence of obesity in the United States was 39.8% in adults and 18.5% in youth.
While obvious factors including genetics, drugs, and other medical conditions may contribute to obesity, behavior is perhaps the most common contributor. Healthy weight on an individual level is associated with a healthy diet and regular physical activity. Restaurants serve incredibly caloric meals, with some meals containing as much as 2,000 calories. The sedentary lifestyle practiced by most adds to the epidemic.
Unfortunately, this obesity trend has spread to other nations, including many developing countries. China, for example, now has more than 5,000 Kentucky Fried Chicken (KFC) restaurants in 1,100 cities. Similarly, McDonald’s expects to have 4,500 restaurants in China by 2022, up from 2,500 in 2017. A growing number of Chinese households also own television sets, personal vehicles, and other technologies that reduce physical activity and facilitate weight gain.
It is of note that economic inequality in developing nations is a primary cause of both overnutrition and undernutrition. Studies conducted in India show that income inequality had the same effect on the risk of being overweight as it did on the risk of being underweight; specifically, for each standard deviation increase in income inequality, the odds of being underweight increased by 19% and the odds of being obese increased by 21%.
While some people have the resources to purchase amounts of food beyond their daily caloric requirements, others cannot meet their recommended caloric intake. However, increasing numbers of poor people are becoming overweight in more nations, as these individuals consume affordable, yet highly caloric meals, such as fast food and processed foods.
An approach to understanding the effects of overnutrition on the metabolic profile is through overfeeding studies. These indicate that overnutrition produces a deterioration of metabolic status. Variability in individual response is however to be expected. Such investigations are potentially useful for identifying those who are particularly susceptible to the development of metabolic risk factors.
The host of genetic factors likely act at tissue levels to influence the response to nutrient excess. Different people may react differently to accumulation of fat, but overnutrition is generally considered to trigger metabolic disorders and predispose one to chronic conditions like Type 2 Diabetes. When choosing what to eat, one should be careful to ensure they choose balanced meals rich in fiber and nutrients and avoid the modern day fast food craze, as the cost of bad eating is too high.