You may have come across several ”raw fooder’ sites describing Edward Howell’s feeding trials of cats with cooked and raw foods. Recently published experimental data show that all nutrients are affected by excessive heat. Due to economic interest, many of these studies investigate the stability of milk proteins.

It has been clearly demonstrated that every high heat process, including pasteurization, decreases antioxidant properties and causes loss of most enzymes and many vitamins (particularly A, E, C, B(1), and folic acid.) Pasteurization is also known to decrease ascorbic acid (vit C), total phenols, and anthocyanins.

High heat causes most prominently starch gelatinization and irreversible protein denaturation (proteins are very unstable at high heat – consider how fast egg white changes its consistency). When exposed to heat, proteins, starches, and non-starch polysaccharides can fragment, creating reactive molecules that may form new linkages not found in nature. Even brief blanching causes leaching of minerals from foods. Furthermore, heat processing causes molecular alterations of the fibers present in food.

The serum protein bovine serum albumin of cows milk is denatured at a temperature of 85 degree C. Heat treatment of proteins (lactablumin, soy protein isolate) at 75 degree C causes formation of unnatural amino acid derivates that may produce adverse and drastic effects on growth, protein digestibility, protein quality, and mineral bioavailability and utilization in rats. At the same time, cysteine, lysine, threonine, and serine are lost in heat processed food.

Excessive heat treatment of infant formulas induces copper deficiency in infant rhesus monkeys. Heat treatment of infant formula and milk causes not only deficient copper plasma levels and reduced bioavailability of amino acids and lysine levels, but also strong protein-protein and protein-lipid interactions. These interactions increase with increasing processing temperature which supports the notion that heat impairs protein digestibility. Damage to food proteins are also explained by complex biochemical reactions between proteins and carbohydrates and oxidation.

Another study confirms that anti-nutritional factors (e.g., oxidized amino acids, D-amino acids, unnatural amino acid derivatives) are formed during heat processing of casein, lactalbumin, soy protein isolate, and wheat proteins. These factors have been shown to be poorly digestible (less than 40%) and their presence significantly reduced protein digestibility in rats and pigs.

Cooking of meat of fish does not only cause denaturing of proteins and formation of anti-nutritional factors, but can also induce formation of potentially carcinogenic compounds.

An in vitro* study shows that pressure cooking, dehulling, germinating, and soaking all improved starch and protein digestibility of beans. However, the most effective improvement in digestibility of starch and protein was brought about by germination, followed by dehulling, and soaking. [* This in vitro study used test tube studies to obtain its data. Test tube results don’t always predict what occurs in vivo.]

The general concept about the effect of heat on proteins might be summarized in a review by Swedish researchers where it is stated that reduced protein digestibility is primarily associated with excessive heat.

This research strongly suggests that heat treatment of pet foods affects almost all nutrients both qualitatively and quantitatively, and also causes impaired protein digestibility. Better options are raw pet foods that contain nutrients in the form with which our pets’ bodies evolved.

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