Biology Reference
In-Depth Information
(
Boden, Rezvani, & Owen, 1984
)
. However, these effects need be con-
firmed in more studies and using different protein types.
5. IMPACT OF PROTEINS AND AMINO ACIDS
ON GLYCEMIA
Research looking at the effects of protein on blood glucose dates back at
least a century with early work carried out on animals. Reilly and colleagues
(1898) treated rabbits and dogs with phlorizin (a competitive inhibitor of
sodium/glucose cotransporter and lowers glucose amounts in blood) and
found that the amount of glucose appearing in the urine was comparable
to the increase in nitrogen appearing in the urine (termed dextrose to nitrogen
ratio or D/N;
Reilly, Nolan, & Lusk, 1898
). The urinary nitrogen increase
represented the dietary protein-derived amino acids that were deaminated
and subsequently converted into glucose and other products. Only urinary
glucose was measured in these studies and it was still unknown then if protein
had an effect on blood glucose concentrations.
Janney (1915)
reported that for
various proteins given orally to phlorizin-treated dogs, the D/N ratio was
unique for each protein, varying from 50% to 80% of the protein given, pre-
sumably due to differences in amino acid composition. In a subsequent study,
Janney showed that the results obtained from phlorizin-treated dogs were use-
ful for studying the impact of dietary proteins on blood glucose in humans
with diabetes (
Janney, 1916
). Different amino acids and their ability to con-
vert into glucose was first documented by
Dakin (1913)
.Theaminoacids
were administered subcutaneously to phlorizin-treated dogs. With the
exception of valine, leucine, isoleucine, lysine, histidine, phenylalanine,
and tryptophan, all other amino acids yielded large amounts of urinary
glucose. This was the first study to suggest that the glycemic potency of
different amino acids were not equal. However, all these studies only
measured urinary glucose.
In 1913, Jacobsen reported that ingestion of egg white protein did not
result in an increase in blood glucose in normal subjects (
Jacobsen, 1913
)
.
Type 2 diabetic subjects ingesting 250 g meat (containing 50 g protein)
showed stable glucose concentrations over the subsequent 5 h (
McLean,
1924
). But when the subject was given 25 g glucose on another occasion
(the amount of glucose that theoretically could have been produced from
the 50 g protein in the 250 g meat), blood glucose concentrations increased
nearly threefold. Another study reported that ingesting 3 pounds of beef
(136 g protein, about 68 g glucose) did not
increase blood glucose
