First division – by firm

This is not really a way to divide the different formulas, but it is of note that there are endless firms producing the different brands, which are available in different countries.

Second division – by indication (or difference in formula constituents):

This is an important part, and to understand it one needs to have basic understanding of the constituents of all the formulas.
All formulas for babies contain protein, carbohydrates (sugars), fats and supplements.

Protein

Proteins in general and amino acids in particular are found in every cell of our body and are required to allow growth.
The two main proteins in breast milk (as in cow’s milk), are casein and whey.
Given that breast milk is considered the optimal nutrition in terms of protein composition, all the usual formulas use these two milk proteins in different proportions as the source of protein. When there’s a reason not to give cow’s milk, it’s possible to give soy-protein based formulas.
So, what is a formula based on hydrolyzed or “broken down” protein? This is a formula in which the cow’s milk protein is simply broken down into smaller pieces. It’s important to know that protein may be broken-down to different degrees:
– Partially hydrolyzed
– Extensively hydrolyzed
– Single amino-acids
Most indications to administer these formulas is some degree of cow’s milk protein allergy, as written in this link.
By decision of the treating physician, it’s possible to consider the extent to which the protein should be hydrolyzed out of the three levels available.
For example, mild sensitivity that manifests as a tummy ache can be approached with partially hydrolyzed formula, whereas in severe allergy that causes respiratory distress, only single amino acids formula should be used. See more details below.

Sugar

The sugar component found in highest proportion in milk is lactose (the milk sugar). This is a disaccharide made of two sugars called glucose and galactose.
Lactose provides the baby with energy, contributes to the proliferation of the (good) gut bacteria and assists with absorption of other building blocks important for the baby’s body.
Therefore, if we understand the main constituents found in formulas (especially protein and sugar), we may divide the different formulas according to the differences in constituents and hence according to the medical indications for each of their use.

Division according to difference in protein

‘Regular’ cow’s milk protein-based formulas – the standard formula that suits most babies.
Soy protein-based formulas – the main difference is the different source of protein (instead of cow’s milk protein there’s soy protein).
Do note that there might be a difference between some of these formulas and regular formulas (based on cow’s milk protein), not only in the type of protein but also in the sugar that the different companies put in and in other components too. But in principle, the main difference is this different protein.
Soy protein-based formulas will also suit babies of vegan families or in specific medical conditions.
On the other hand, there’s no reason to prefer feeding with this formula compared with regular formula.
Another point is sensitivity to cow’s milk protein that babies sometimes have. However, given that in many cases there’s also cross sensitivity to soy protein, changing the formula to soy-based one needs to be considered with prudence by the family and treating physician.
In some cases, this change will not make any difference.
Formulas based on hydrolyzed cow’s milk, as already mentioned earlier, there are three degrees of hydrolysis:
Partially hydrolyzed – supposedly, made for babies that are suffering from milk sensitivity/allergy to cow’s milk protein, manifesting only as abdominal pain. In practice, none of them presume to offer a true solution for babies with real sensitivity to cow’s milk.
These formulas are practically used as an alternative formula for babies suffering from stomach ache. Usually, in real sensitivity to cow’s milk protein, these formulas will not be recommended by the treating physician. These formulas (as opposed to more extensively hydrolyzed formulas as you will see later on), to not require a doctor’s prescription.
Formulas based on extensively hydrolyzed cow’s milk – made for babies suffering of real but moderate cow’s milk protein allergy/sensitivity and also cross sensitivity to soy protein. These formulas require a prescription.
Amino-acid based formulas – made for babies suffering from certain intestinal diseases or severe sensitivity/allergy to cow’s milk and soy proteins. This is a formula in which the amino acids (building blocks of proteins), are separated and are found in their molecular form (Neocate for example). In most settings, these formulas require a prescription.

Division according to difference in sugars

Low or non-lactose formulas will use less (or no) lactose. The substitute sugar will be different between the different firms, ranging from maltodextrin, that is a chain of sugars extracted from corn, to glucose syrup solids and in some cases even sucrose (white sugar).
There are clear instructions by the health authorities as to the types of sugar substitutes to be used – for example, glucose syrup solid is a polymer of glucose and is permitted for use in formulas starting at stage 1, compared with sucrose that is not permitted at that stage.

Other formulas suitable for other specific indications

Anti-regurgitation (anti-reflux) formulas – these are cow’s milk protein-based formulas that use potato or rice starch that transforms into a sort of thick dough in the acidic stomach environment and reduces reflux of food backwards up the esophagus. Another option is using a dissolvable fiber that thickens the formula in the bottle and is unaffected by the stomach’s acidity. You can read more of reflux (spit-ups) in babies in this link.
Post-discharge preemie formulas – essentially, these formulas are similar in contents to regular formulas but are rich in energy and protein and fortified with minerals, vitamins and other elements. The decision to use a regular formula or one that is designed for preemies for a premature baby that is not breast-fed (breast milk is the best nutrition for preemies similar to other babies) is affected by many factors and will be made by the neonatology or newborn unit team discharging the baby from the hospital after birth.

Other additional components in babys formula that are good to know

– LC-PUFA – or in their full name, long-chain polyunsaturated fatty acids – are certain fatty acids that have been proven lately to assist in the development of the nervous and visual systems.
These fatty acids are found in breast milk and in fact, in all recognized formulas in developed countries (there are differences between products in the amount added).
– Prebiotics – a component found in breast milk and is made out of long chains of sugars that provide substrate for good bacteria growth in the intestines and are important for the development of the digestive and immune systems.
Common prebiotic components that are often used in formulas are FOS and GOS and are use in different proportion and amounts by the different firms.
– HMO (Human milk oligosaccharides) – chains of sugars that unique active components of breast milk (over 200 different compounds) and are the third most abundant component of breast milk after lactose and fat (of the dry, water-less material).
They have an important role in the development of the digestive and immune systems.
Protective immunity is achieved by several mechanisms, one of which is the prebiotic mechanism as a substrate for friendly bacteria in the gut.
– Probiotics – probiotic bacteria are friendly bacteria that have a beneficial effect on the host, babies acquire these bacteria in the birth canal and after that, through breast-feeding.
The gut of breast-fed babies is rich in probiotic bacteria, in particular of the Bifidobacterium and lactobacillus types.
Studies show that an environment rich in probiotic bacteria contributes to the maturation of the digestive system and the development of the immune system.
Different types of probiotics are added to some of the formulas, some of them from the age of birth and in some in later stages.
– Palm oil – some firms advertise being palm oil-free. Palm oil is a source for fatty acids in formulas. Most baby food firms in the world use a mixture of fats, also including palm oil, aiming to get close to the fat composition in breast milk.
Palm oil was not proven as a substance that is dangerous for babies and therefore in my opinion there’s no benefit nor disadvantage to adding or removing palm oil from formulas.