GASTRIC ACIDITY & MIXED FEEDING
We are often asked about the science behind our raw feeding advice.
We advise people to make a choice between raw-food and processed food – but not to feed a bit a both.
Here is an explanation for our advice.
Click on this info-graphic for a summary of our advice:
And below is an explanation of the scientific studies and papers (click on the title to access the whole paper) that support our advice...
Saint-Hilaire, S.,Lavers, M.K., Kennedy, J. & Code, C.F. Gastroenterology 39 (1) July 1960
Carnivores require highly acidic gastric (stomach) contents following a meal, in order to promote safe and effective digestion.
The effect of protein, relative to other foods, on gastric acidity has long been known. A pivotal study by Saint-Hilaire et al (1960) used gastric pouches to measure the acid-stimulating effects of different foods.
“The foods with the highest secretory equivalent values belonged in the meat, fish, and dairy products categories.”
The foods with the least ability to stimulate acidity had the most carbohydrate content: fruit, bread, cereals, green peas, oatmeal and potatoes. Most of these foods are common ingredients in processed petfoods.
It was concluded: “protein was the most important acid-stimulating factor.”
Lennard-Jones, J.E., Fletcher, J. & Shaw, D.G. Gut (BMJ) 1968 9 177-182
Ingested food stimulates the production of acid within the stomach.
This acidity needs to be reduced (buffered) after the food moves through to the small intestine, in order to avoid damaging the intestinal wall (causing or exacerbating ulcers).
Lennard-Jones et al (1968) found that protein was both the best stimulator of gastric acidty, and the best buffer: “The output of acid from an innervated canine gastric pouch is directly proportional to the nitrogen content of meals entering the stomach. The buffering power of meals also depends on their protein content. High protein meals thus stimulate much acid secretion by the gastric mucosa and also buffer the acid secreted.”
They also raised an important point about the form of food. A highly processed diet requires little chewing, and therefore stimulates less saliva production than a raw, meaty bone diet.
“Malhotra (1964) suggest that the saliva secreted during mastication buffers gastric acid and that foods which are swallowed with little or no mastication become mixed with little saliva and therefore buffer less acid. The consistency of a meal may thus affect the subsequent acidity of the gastric contents.”
Lichtenberger, L.M., American Journal of Physiology 243, G429-441, 1982
Lichtenberger (1982) described the importance of the hormone, gastrin.
Gastrin regulates the acidity of the stomach following a meal. It also plays a role in the rate of food leaving the stomach, and cell health within the gastrointestinal tract. If gastrin secretion is not appropriately regulated, there can be serious outcomes:
“abnormalities in gastrin homeostasis may accompany gastrointestinal disturbances associated with various disease states, including…diabetes.”
Gastrin levels are elevated following a meal. This response is regulated by the types of nutrients that come into contact with the G-cells of the stomach (cells which release gastrin). The amount of gastrin secreted is determined by the nutrient composition of the meal:
“A number of studies on a variety of animal species, including humans, have demonstrated that the food-induced rise in serum gastrin levels is primarily dependent on the presence of protein in the diet”
Protein is known to be the most potent stimulator of gastrin (carbohydrate is a poor stimulator). The form of protein also plays a part. Lichtenberger described how the protein in a commercial synthetic diet is not a good stimulator of gastrin:
“serum gastrin concentrations fail to be maintained at the levels normally recorded in animals fed standard rat food, if rats are placed on one of several commercially available synthetic or semi-synthetic diets. This decline in blood gastrin levels was not attributable to quantitative differences in dietary protein content. This was clearly indicated by the findings that serum hormone levels were abnormally low in both a group of rats that consumed a protein-defficeint diet… and in a group of animals fed an isocaloric amount of a high protein formulae.”
He proposed that: “many synthetic diets that are composed of either free amino acids or casein as their protein source are deficient in an unknown proteinaceous constituent that is required for gastrin release.”
Processing may render the protein less effective. Lichtenberger found that: “lyophilization(freeze-drying) resulted in a significant 50% reduction on the diet’s ability to stimulate hormone release.”
Frank P Brooks American Journal of Clinical Nutrition 1985; 42: 1006-1019
Brooks (1985) also examined the effect of diet on gastric acidity.
He too found that protein was both the strongest stimulator of gastric acidity, and the most effective buffer, thus protecting the small intestine from damage and ulceration.
Brooks also touched on the impact of palatability on acid stimulation. A more appealing meal leads to greater stimulation. This is a particularly important consideration for the many pets out there that reluctantly eat their processed food (or turn their noses up at it altogether).
“An appetizing meal can stimulate acid secretion during sham-feeding to a greater degree than routine institutional food.”
In patients with small intestinal ulcers, Brooks notes that: “appetizing diets, high in calories and protein content, are both better buffers of gastric HCL and more powerful stimulants of acid secretion.”
DelValle, J. & Yamada, T. Journal of Clinical Investigation Jan 1990 85 139-143
DelValle and Yamada (1990) also found that: “proteins are the primary food constituents found to have an acid secretagogue action, it is not surprising that only proteins are capable of significantly stimulating gastrin secretion.”
They noted a dose-dependent response between amino acids and amines (the constituents of proteins) and the strength of gastrin stimulation. A high concentration of these constituents was required to adequately stimulate gastrin.
A minimally processed prey-based diet will provide a carnivore with normal (appropriate) levels of protein, thus supporting optimal gastric acidity. Most processed, commercial diets are low in protein (because they are high in carbohydrate – a cheaper way to construct a diet).
Ewen Callaway, 26 November 2014, Nature
We advocate feeding a diet that promotes a highly acidic stomach for carnivores. One of the reasons for this is safety. Some people worry about the risk of illness from Salmonella. This is a common concern for biscuit-fed pets, as there are regular biscuit re-calls due to Salmonella contamination. There is also potential for Salmonella on a raw diet if it is not well sourced and stored.
An acidic stomach is a clever evolutionary trait that allows carnivores to safely consume bacteria that might cause harm in a less acidic gut environment.
The article in 'Nature' details how wild vultures (carnivorous scavengers) provide an excellent example of the benefits of this adaptation. They often eat dead or decomposing animals, and are exposed to toxins as potentially deadly as anthrax (Bacillus anthracis) – yet they are able to thrive on this diet due to their highly acidic stomach and the right balance of gut microbes.
The Role of Gastric Acid in Preventing Foodborne Disease and How Bacteria Overcome Acid Conditions