The mouse study found that the protein – soy-ghretropin – works by increasing release of the ‘hunger hormone’ ghrelin in the stomach.
If proven successful in humans, it could be the first food-derived peptide to increase appetite via the ghrelin pathway, the team writes in FEBS Letters.
“Soy-ghretropin may be developed for elderly people or anorexic patients whose plasma ghrelin levels and food intake are reduced,” wrote the researchers led by Junya Nakato of the division of food science and biotechnology at Kyoto University in Japan.
The idea that a foodborne nutrient could stimulate appetite through increasing the release of ghrelin is indeed interesting for hunger-suppressed patients, professor Christian Benedict, department of neuroscience at Uppsala University in Sweden said.
“Ghrelin possesses strong appetite-stimulatory properties,” he told FoodNavigator. “People may prefer such food-based proteins (over non-food based nutrients) since they are made up of a plant.”
However, Benedict stressed that human studies will be needed before soy-ghretropin’s effects are confirmed.
The team identified soy-ghretropin – a 22-amino acid – as a peptide corresponding to the beta conglycinin alpha-subunit, which is related to the secretion of ghrelin.
Male mice were used for the study, with blood samples to test ghrelin levels taken 60 minutes after the animals ate soy-ghretropin.
Food intake analysis involved feeding the mice a protein powder with 0.0003% soy-ghretropin content. Food intake was then measured after 24 hours.
The team found that “orally administered soy-ghretropin increased plasma ghrelin levels and food intake.”
A new option?
Several previous studies suggest that plasma ghrelin levels are reduced in the elderly, which the current researchers say may contribute to the “anorexia of ageing”. Ghrelin has also been linked with reducing impulse control, which could be connected with eating disorders.
Circulating levels of ghrelin are said to rise before eating or during fasting, and hormones produced in the body which are linked with its release include norepinephrine and glucagon.
However, prior to this study there has been little research into ghrelin stimulants not produced in the body, the team said.
Other options used for weight gain have included some antidepressants, for which there is limited evidence in anorexia nervosa patients, Benedict said.
Several reports also suggested pharmaceutical company Eli Lilly’s antipsychotic medication olanzapine (Zyprexa) was successfully used in stimulating appetite and weight gain among cancer and anorexia patients, he added.
“There are however large inter-individual differences in the response to these drugs. That is to say, there is always a need for new options, as it may help combat weight loss in patients with poor responses to other appetite-stimulating drugs,” Benedict said.
However, he said long-term interventional studies in healthy humans followed by clinical trials in patients with weight maintenance issues are needed. The research should examine the role of age, gender, time of day and interactions with other food components.
Further, this study only looks at male mice, which limits information on factors such as how menstrual cycle could alter soy-ghretropin’s affects, he added.
Source: FEBS Letter
Published online first, doi: 10.1002/1873-3468.12306
“Soy-ghretropin, a novel ghrelin-releasing peptide derived from soy protein”
Authors: Junya Nakato, et al.