Welcome to the internet, the land of misinformation where in the absence of facts experts abound!
NLS does not cause fatty liver disease, and many people (myself included) have tanks full of mature fish where NLS has been fed exclusively for several years. (including those classified as strict herbivores)
I've been feeding a mix of carnivores, omnivores, and herbivores an exclusive diet of NLS for the past 5 years, and I have seen the results of fish that have been on this same diet for years longer than my fish, and have yet to see, or even hear of any type of premature death in anyones fish, let alone any cases of fatty liver disease.
In the wild, the cichlids found in the Rift Lakes have evolved & adapted to living in certain niches of the lake, which over time has forced them to become specialized feeders. (as per Ad Konings) Yet all of these specialized feeders will readily eat anything that's available. (as per Ad Konings)
While a fish classified as a strict herbivore (such as a Tropheus moorii) may indeed spend its entire day scraping the aufwuchs, I can assure you that they would much rather eat a handful of worms if given the opportunity. In the wild they eat low quality foods because that's the only foods available, not because they choose to!
And while certain species such as Tropheus sp. may in fact be classified by the scientific community as strict herbivores, the reality is that even though algae dominates the stomach contents, the actual foods that make them grow are insect nymphs and larvae, crustaceans, snails, mites, micro-organisms, and zoo plankton, not vegetable matter. (as per Ad Konings)
Their long digestive tracts are designed as such so that in nature they can break down the complex plant matter that they consume, which doesn't mean that they can't properly assimilate more easily digestible forms of protein. Apparently this is a concept that some hobbyists fail to grasp.
Keep in mind that the vast majority of fish are opportunistic feeders, and are all omnivorous to a certain extent. Cichlids classified as carnivores don't just eat meat, any more than a herbivorous cichlid just consumes vegetable matter.
Taking another fish classified as a herbivore, the Atlantic Blue Tang, although they too are indeed algae browsers, through feed trial studies we now know that they require much more than algae to be maintained long term in captivity.
Several years ago Dr. Ruth Francis-Floyd from the University of Florida performed a study on the captive nutritional management of herbivorous reef fish. She used Atlantic Blue Tangs as her test subjects, and this study clearly proved that this species would not do well on seaweed alone. On this so called "natural" diet of washed seaweed, over the course of a few months the fish suffered a large mortality rate of approximately 80 percent, with the surviving fish all showing clinical signs of malnourishment.
I look at it this way, all wild fish are opportunistic feeders, and will eat pretty much anything that comes their way, and while herbivores may in fact consume large amounts of plant matter, and carnivores may in fact eat large amounts of fish based foods, that plant matter often contains certain amounts of nymphs, larvae, crustaceans, snails, mites, micro-organisms, and zoo plankton, and the smaller fish that the larger carnivores consume are typically gut loaded with phytoplankton (which consists of microscopic plants), so in actuality all of the Rift Lakes cichlids consume the same types of protein, fats, carbs, etc, just in varying degrees.
Fish simply excrete excess protein, it doesn't build up in dangerous levels as excess fat can, so you're certainly not harming a herbivore IF you feed a slightly higher protein content than what that fish would typically eat in the wild.
This is yet another one of those urban legends about herbivorous cichlids, that being that foods that are high in protein cause bloat, which for the most part is total nonsense. Foods that are high in poorly digestible grains may cause dietary bloat, but protein itself is not the enemy.
Now if one considers the fact that high quality proteins such as krill, herring, mussel, etc, are THE most expensive raw ingredients used in ANY commercially prepared fish food, it only stands to reason that no fish food manufacturer in their right mind is going to use excessive amounts of these raw ingredients. This is exactly why some manufacturers use low cost protein sources and also boost the crude fat percent so that there's no chance that the more costly protein will ever be utilized as an energy source. (they save $$$$)
In other words, in the case of excess protein in commercial fish foods, for the most part you are worrying about nothing.
In the case of excess protein in NLS, I guarantee you that you are worrying about nothing.
With only 5% crude fat, it's an absolute guarantee that pretty much all species, especially high energy species, are going to cut into some of the protein as an energy source. While most manufacturers might view this type of feed design as poor business, or a waste of potential revenue (as fat is far less expensive than protein) Pablo has always put the health & well being of the fish at the forefront.
And kudos to him for doing so.
Fatty liver disease (which isn't actually a disease) is caused by a diet that is excessive in fats, and/or grains, which are stored as fat if not used immediately as an energy source.
If/when excessive protein is consumed by a fish, it is deaminated & excreted as waste. While this process does require energy, and can cause a reduction in growth of the fish (if excessive), and will add unwanted polution to ones tank, with New Life's cichlid formula being in the 34% protein range this is obviously not a cause for concern. There are quite a few raw ingredients that make up this formula, beyond Antarctic Krill.
HTH
