Mimicking breast milk fat is much more than just a similar fatty acid composition. The molecular structure of lipids has significant effects on their nutritional properties and health effects. Cow milk fat has many natural similarities with human milk fat both in composition and structure.
To me, human milk is the greatest mystery of nature and the most fascinating food. Breast milk is the best food for babies*. In recent years, there has been a lot of discussion on the fats used in infant formulas, as research has increased our knowledge about specific fat compounds in breast milk and of their significance for infant health and development.
Fat is an important element in infant formulas. It is second in abundance and provides about a half of the energy content of formula. Many formulas contain only vegetable oils as the source of fats, whereas others are milk fat based. The aim in formula production is to simulate the golden standard, the breast milk fat.
The complexity of breast milk comes from the large variety of fatty acids present and the specific distribution of the fatty acids in the fat molecules.
Both human milk fat and cow milk fat have a highly complex fatty acid profile. Both contain over 200 different fatty acids, and not only the common ones but the uncommon ones. In vegetable oils, the fatty acid composition is much simpler.
Medium chain fatty acids are fatty acids where the carbon chain is between 6 and 12 carbons. Human milk fat and cow milk fat have a high content of medium chain fatty acids, whereas in vegetable oils these fatty acids are commonly missing. Some exceptions are coconut oil and palm kernel oil where the content of medium chain fatty acids is high.
The fat digestion in infants is different to the fat digestion in adults, as the pancreatic lipase is not fully developed yet. Fats rich in medium chain fatty acids are digested faster by infants than long chain fatty acids. After digestion, medium chain fatty acids are also absorbed faster. Within the cells where energy is needed, the medium chain fatty acids are oxidized faster than long chain fatty acids.
Medium chain fatty acids are a faster and more efficient source of energy for infants than long chain fatty acids.
The position or distribution of the fatty acids in the fat molecules varies. For example, in human milk fat a very important fatty acid, the palmitic acid, is in the middle position, also called sn-2 position. Whereas in vegetable fat it is typically in the outer positions what we call sn-1,3 positions.
The palmitic acid distribution has a very profound impact on infant nutrition. If palmitic acid is located in the outer positions, as in the case of POP, after digestion free palmitic acid will be released, and the middle oleic acid will remain in the monoacylglycerols. The oleic acid will be absorbed efficiently. But the free palmitic acid will meet the calcium ion in the food, and the palmitic acid and calcium ion will together form insoluble calcium soap. The soap will not be absorbed but is secreted in feces. This results in poor absorption of lipids and poor absorption of calcium, a nutrient which is very important for infants’ bone growth and health.
In the case of OPO, the palmitic acid is located in the sn-2 position. The molecule has two oleic acids in the outer position and the palmitic acid in the middle position. After the fat digestion, we will have free fatty acids released as oleic acid. Oleic acid does not form calcium soap as palmitic acid does. This results in better absorption of palmitic acid and oleic acid, and also in better absorption of calcium.
In cow milk fat, the position of palmitic acid is closer to what is found in human milk. About 40% of the palmitic acid is in the sn-2 position. In the human milk it is higher, over 70%. In vegetable oils it is less than 10%.
MFGM is a treasure chest of bioactive lipids. The major lipids on the MFGM are cholesterol, sphingolipids, and phospholipids. The content of cholesterol is about 120-150 mg/L of milk, and the content of the rest of the lipids is about the same, 150-200 mg/L. This level is surprisingly similar in human milk and in bovine milk.
There are many studies showing the positive health benefits and importance of the milk globule membrane lipids for infants. Many of the health benefits have been confirmed in clinical studies. These include benefits related to neurodevelopment, brain function, cognitive function, immune function, and gut health.
Cholesterol is a very important nutrient for infants. In human milk and in cow milk, there is quite high content of cholesterol. This is because cholesterol is:
If infants are fed with formula low in cholesterol, the infants’ body will compensate this by increasing the internal cholesterol synthesis to achieve the high cholesterol level in the blood. Long term upregulation of cholesterol synthesis increases the risk of cardiovascular diseases in later life.
For that reason, we should have MFGM lipids included in infant formula. Clinical studies have shown that adding MFGM fraction from the bovine milk will increase the cholesterol level in the blood without activating the cholesterol biosynthesis in infants.
*Using infant formulas is second to breastfeeding, a fact supported by WHO. Babies should be breastfed exclusively for 6 months, with continued breastfeeding after introduction of complementary food. A healthcare professional should be consulted before introducing infant formula or complementary food to a child’s diet.