Mother’s milk protects infants from infection

We live in a sea of microorganisms; they are in the air we breathe, the food we eat, the water we drink, and even live on our bodies. Some of these microbes are relatively harmless and can even be beneficial, while others can cause sickness and death. For the most part, our immune system protects us from infection from the more malevolent varieties.

When an infant is born, it comes from the relatively sterile environment of the womb into a world that is teeming with potentially harmful germs. At this stage of life the immune system is not fully developed and the infant is highly vulnerable to infection. Fortunately, infants are not born defenseless; mother’s milk contains several substances that protect infants from infections during this critical time. Some protection comes from the mother’s antibodies in her milk, but perhaps the greatest protection comes from its fat content.

Mother’s milk is rich in fats, mostly saturated and monounsaturated fats, with some polyunsaturated fat to supply the infant’s essential fatty acid needs. These fats serve multiple functions; they provide nourishment, help to establish a healthy gut microbiome, and ward off infection and disease.

Long chain fatty acids (LCFAs) from our foods modulate intestinal immune function, which is independent of the systemic immune system. The absorption of LCFAs stimulates the influx of lymphocytes, a type of white blood cell, through the intestinal wall. This process helps defend against potentially harmful microorganisms that may have found entry into the gastrointestinal tract from the meal.¹ Germs can be carried into the body by any type of food – milk, vegetables, fruits, grains, and so forth. Including some fat with meals helps protect against infection. Mother’s milk naturally supplies the fat necessary to do this.

Fatty acids kill disease-causing microorganisms

In addition, many fatty acids, especially those in breast milk, possess potent antimicrobial properties capable of killing troublesome bacteria, viruses, fungi, and parasites. These fatty acids are powerful enough to kill intestinal troublemakers like E. coli, H. pylori, and Candida albicans, yet completely harmless to human cells. Unlike antibiotics that kill all bacteria, fatty acids are more selective; they can kill the major troublemakers yet leave the good bacteria alone. In this way, potential troublemakers are suppressed while the good microbes are allowed to thrive and firmly establish themselves in the infant’s digestive tract, producing a healthy gut microbiome.

The fats we eat are composed of triglycerides. Triglycerides consist of three fatty acids joined together by a glycerol molecule. When fats are consumed and digested, the triglycerides are gradually broken down into diglycerides (two fatty acids joined by a glycerol), monoglycerides (one fatty acid attached to a glycerol), and individual fatty acids. It is the monoglycerides and fatty acids that have the antimicrobial properties. Triglycerides and diglycerides have none.

Some fatty acids are more effective at killing certain types of microorganisms than others. Some kill bacteria like E. coli, others kill streptococcus and staphylococcus, and still others yeasts and viruses. For example, capric acid, a 10 chain saturated fatty acid, is more effective at killing certain bacteria than caprylic acid, an 8 chain saturated fatty acid; however, caprylic acid is more effective at killing certain fungi than capric acid. Natural fats contain a mixture of several different types of fatty acids, so they are effective against a wide variety of pathogens.

Fats boost immune function

The antimicrobial effect varies greatly among the different fatty acids. Some are very potent while others are rather weak. Some LCFAs that are common in our everyday foods, such as oleic and linoleic acids, possesses some antimicrobial effects. However, medium chain fatty acids (capric, caprylic, and lauric acids), display the greatest antimicrobial activity, with lauric acid and its monoglyceride – monolaurin – having the strongest overall effect. Medium chain triglycerides are important components of mother’s milk. Medium chain fatty acids (MCFAs) also stimulate the production of white blood cells, boosting immune function. These and other fatty acids are essential in establishing the infant’s gut microbiome and provide protection from systemic infections.

Adults also benefit in a similar manner from the antimicrobial properties of fatty acids through the consumption of fats and oils. After weaning, we no longer enjoy the benefits of mother’s milk and the MCFAs it contains, but we can get MCAs through the consumption of dairy, as all mammal milks contain these protective fats.

Other than dairy, there are only a few good dietary sources for MCFAs. The best natural sources are coconut and palm kernel oils. Coconut oil is by far the richest natural source, with even more than that found in mother’s milk. Coconut oil is composed of 63 percent MCFAs, with lauric acid comprising almost 50 percent. Palm kernel oil contains 53 percent MCFAs, with lauric acid making up about 45 percent. In comparison, butter, which is the third richest source, contains only 8 percent MCFAs. Most of the other fatty acids (long, medium, and short) possess varying degrees of antimicrobial fighting power and when consumed together, work synergistically to help protect us from infection.

Germs are everywhere. No matter how hard you try to scrub your dishes, clean your hands, and wash your food, germs are always present. Acids in our stomach kill most germs, but some manage to slip by to disrupt the gut microbiome or cause illness. The fats in our foods act as a secondary means of protection. In the digestive tract they destroy disease-causing organisms on contact. Fatty acids in the bloodstream help fight off systemic infections.

Unlike antibiotics, which kill only bacteria, fatty acids are effective against bacteria as well as viruses, fungi, and some parasites. For generations mothers have given their families homemade chicken soup to fight off the cold or flu (viral infections). As it turns out, a handful of scientific studies show that chicken soup really could have medicinal value.^{2, 3, 4} Although these studies do not identify the exact ingredient or ingredients in the soup that make them effective, it might possibly be the fat. Homemade chicken soup is generally a rich source of fat.

So, when you eat a meal containing fat, you are eating food that will protect you from many forms of food poisoning and infectious disease. If, on the other hand, you avoid fat and eat low-fat foods, you are making it easier for germs to survive in your digestive tract and cause trouble. A healthy diet always includes ample amounts of fat.

HDL cholesterol protects against toxins

Saturated fats, and particularly lauric acid, increase the production of HDL cholesterol.^{5, 6} This is important because HDL has been shown to help protect against cardiovascular disease, reduce inflammation, and aid the immune system in fighting infections. HDL plays an important role in our defense by absorbing toxins produced by bacteria and transporting them to the liver where they are neutralized and excreted from the body.^{7, 8} Much of the harm caused by bacterial infections comes from the deleterious effects of bacterial endotoxins. HDL mops up these toxins and clears them from the body. Both animal and human studies have shown that higher HDL levels increase resistance to and reduce the risk of death from bacterial infections.^{9, 10} HDL is not only protective against bacteria, but has also been shown to inhibit the ability of certain viruses to penetrate our cells and to play an important role in defending against parasitic infections. Eating saturated fat or a low-carb diet have both been shown to be the most effective ways to increase HDL levels.

LPS activate an immune response

The antimicrobial properties of dietary fats help train our immune system during infancy and keep it in good working order throughout life.

When we eat a meal, protein is broken down into amino acids and fat is broken down into fatty acids, making them small enough to penetrate the intestinal wall. Inside the intestinal wall, fatty acids and amino acids are combined into little bundles of fat and protein called chylomicrons. These chylomicrons travel from the lymphatic system to the bloodstream, where they circulate throughout the body delivering fat and protein to wherever they are needed.

As triglycerides are broken down in the gastrointestinal tract, fatty acids are released. Certain saturated and unsaturated fatty acids kill potentially troublesome bacteria. Many of the bacteria that are destroyed have an outer cell membrane composed of lipopolysaccharides (LPS). Some LPS fragments from the destroyed bacteria are small enough to pass through the epithelial lining and into the intestinal wall. Here the fragments are picked up with fatty acids, amino acids, and other substances and packaged into chylomicrons and are eventually carried into circulation.¹¹

In the bloodstream, LPS is recognized as a foreign invader – a bacterium – and stimulates an immune response. Because of this process, some authors and researchers have suggested that eating high-fat diets promotes systemic inflammation leading to the development of obesity, diabetes, heart disease, and other disorders associated with chronic inflammation. They claim that dietary fat, particularly saturated fat, is inflammatory, and therefore causes chronic inflammatory related disease. In their zeal to find reasons to condemn dietary fat, the obvious is overlooked, as we shall see below.

Fat is an important part of a healthy diet

Fat has always been an important part of the human diet. Some populations, such as the Inuit, native Siberians, the Maasai of Africa, and many others subsisted and thrived on very high-fat diets. Over the past century thousands of people have adopted a very high-fat, ketogenic diet, some for extended periods lasting many years, and have not experienced obesity, diabetes, or heart disease. In fact, just the opposite happens; those on ketogenic diets generally lose excess weight, develop better blood sugar control, and reduce their risk of heart disease. The high-fat diet didn’t harm them, but made them healthier.

Fats are essential in establishing a healthy gut microbiome in newborn infants and in maintaining a healthy microbial population throughout life. The absorption of LPS is a normal and universal process that occurs in both humans and animals.¹² It is not a defect in biology or some freakish abnormality caused by eating fat. In animals, the process is the same. Carnivores and some omnivores, for example, eat a lot of meat and fat but do not become obese or develop diabetes or heart disease. However, dogs and cats fed pet foods high in processed grains, legumes, and other carbohydrates with only moderate fat, often do develop these human diseases. Obviously, meat and fat do not cause these problems in animals or in humans.

Fatty acids train the immune system

In the body, when a white blood cell senses the presence of LPS, it interprets it as an invasion by potentially harmful bacteria and initiates an immune reaction by activating an inflammatory response and stimulating the production of more white blood cells and HDL cholesterol to defend the body. This is the body’s normal reaction to a potential threat. Contrary to popular belief, inflammation isn’t something that is bad or evil, it is the normal process in which the body mounts a defense and fights off infection. In most cases, it is a good thing, as it is protecting the body. Only when inflammation becomes chronic and never shuts down does it become a problem. This only happens when there is a stimulus that constantly triggers inflammation, such as chronic infection or tissue irritation. The slight inflammatory reaction from LPS after eating fat is usually only temporary and not a chronic condition even when fat is consumed at every meal. Interestingly, people who have been on very high-fat diets (60-80 percent of total calories consumed) for awhile generally have optimal C-reactive protein (CRP) levels. CRP is a marker for systemic inflammation. Those people who are diabetic, overweight, or at high risk for heart disease, have distinctively elevated CPR levels, indicating chronic inflammation.

While the consumption of some types of fatty acids do raise blood levels of LPS, markers for inflammation remain unchanged, indicating that high-fat meals do not trigger systemic inflammation, although there may be an increase in white blood cell production.¹³ LPS can stimulate an inflammatory response, especially when it is associated with living bacteria, but apparently when the source of the LPS follows a fatty meal there is little or no accompanying inflammatory response. This is probably because LPS is from bacteria that are already dead and so there is no threat of an infection.

These LPS fragments trigger a mild immune response, which includes the increased production of white blood cells. White blood cells are the workhorse of our immune system and an increase in their numbers enhances immune function. More immune cells on the job means more cells are at work, seeking out and eliminating all potentially harmful troublemakers, not just bacteria, but viruses, yeasts, parasites, toxins, cancerous cells, and LPS fragments.

Instead of being a defect caused by a high-fat diet, the absorption of gut-derived LPS fragments is a normal and even necessary process of biology. LPS makes up the outer cell membrane of many pathogenic bacteria and is not the whole living organism. LPS is often used in medical research as a means to stimulate an immune response without the threat of causing an actual infection. Unlike living bacteria, it can’t multiple and grow. It is defenseless against the immune system.

For this reason, LPS provides a valuable tool to condition and train the immune system without danger. This is especially important in infants, whose immune systems are still developing and learning how to recognize harmful substances. Nursing infants eat a very high-fat diet. About 56 percent of the calorie content in human breast milk comes from fat, half of which is saturated fat. Many of these fats have the ability to kill potentially harmful bacteria in the gut. LPS fragments from the dead bacteria are then absorbed into the bloodstream and initiate a mild immune response. This way the infant’s immune system is trained to recognize harmful microorganisms. The slight increase in white blood cells boosts immune efficiency and the clearance of microbes and toxins from the bloodstream. This process continues in adults, keeping the immune system sharp and ready to leap into action whenever living invaders enter the bloodstream.¹⁴

LPS in large numbers, due to an active infection, can make you sick, but the small amount that enters the bloodstream from the digestive tract is too small to cause any noticeable symptoms or any harm. The release of LPS into the body from the gut is a normal, natural, harmless process. It couldn’t be otherwise, as this process occurs in all infants. Mother’s milk contains fats that kill potentially harmful bacteria in the gut. This releases LPS into the body. If this process was harmful, as some scientists have proposed, it would be very detrimental to newborn infants, whose immune systems are not yet completely functional. On the contrary, exposure to LPS helps train the infant’s immune system to recognize and mount a quick response to infection without the danger of an actual infection. This process is extremely important in developing our immune system as infants, and as adults it keeps our immune system in good working order. Dietary fats, and especially MCFAs, serve a very important role in training and maintaining proper immune function.