Oils of garlic and onions shown to blunt effect of high fat diet in rats
The various health properties of garlic and onions have been studied for years. Researchers have looked at how these ingredients function in the diet by boosting absorption of key compounds.
They have also investigated how components of these botanicals function in the blood by exerting antioxidant effects and affected blood lipid levels.
For example, one study conducted in India in 2008 found in a mouse model that the two ingredients together reduced the incidence of gallstones associated with high cholesterol levels (80% of gallstones are associated with this condition).
Another study from 2010, also done in India, found that garlic and onion together helped significantly boost the absorption of certain minerals such as zinc and iron found in common staple foods such as rice and chickpeas. Researchers in that case used a model of mouse intestines for their study. In South Korea in 2012 researchers looked at how supplementing the diet with onion and extracts of the botanical could protect brains against stroke damage due to these ingredients’ antioxidant potential. That study was done on live mice.
The most recent study, conducted by researchers in Nanjing, China, differed in that the team took a step up in their animal models by using rats. The researchers also used the oils of the two substances, rather than incorporating the foods into the study animals’ diets in whole or granular form.
Long history of use, long list of beneficial compounds
Both botanicals have a long history of use in TCM, and are gaining in popularity on the world market. The study notes that garlic production has been increasing in China. The country now accounts for one-third of the world’s total acreage of the crop.
“The four most important organosulfur compounds, considered to be the major biological agents [in garlic], are diallyl sulfide (DAS), diallyl disulfide (DADS), diallyl trisulfide (DATS) and allylmethyl trisulfide. A series of biological benefits, such as hypolipidemic and hypocholesterolemic effects, antioxidant potential, and antimicrobial activity, have been reported. The pungent fractions of garlic are mostly sulfur-containing moieties, while its two chemical groups, namely, flavonoids and ALK (EN)-based cysteine sulfoxides (ACSOs), have marked effects on human health,” they noted.
Similarly, onion production has been ramping up, too, with the world total output now reaching 44 million tons, a 25% increase over the past decade. Onion, too, has a lengthy list of health promoting properties associated with it.
“Onions contain a considerable number of compounds that are highly beneficial for human health and that have been reported to have anti-hyperglycemic and anti-hyperlipidemic effects on diabetic rats. ACSOs are also some of the active components in onion oil. The main components of onion oil are sulpho compounds, including propane disulfide, disulfide propylene, S-methyl cysteine, and others,” they wrote.
Essential oils used in study
In the Nanjing study the researchers obtained oils from the fresh bulbs of the two botanicals using a steam distillation technique used for extracting essential oils. The chemical composition of the resulting oils was tested and matched results obtained in previous studies done by the same group, the study said.
The researchers used 96 Sprague-Dawley rats that were divided into eight groups.
The subdivision was done to test the success of the high fat diet in achieving a hyperlipemia state. It also enabled the researchers to test different dosages of the onion and garlic oils and to eliminate the possible effects of the method of administration, in which the oils were dissolved in polysorbate 80, a common food surfactant.
The researchers found that the rats supplemented with garlic oil and onion oil gained less weight on the high fat diet compared to their peers. They also escaped the liver-damaging effects of the diet.
“This study may have important implications because it is the first report demonstrating that garlic oil and onion oil have anti-obesity effects and improve the lipid profile in high-fat diet fed rats. However, further study is needed to investigate which compounds in garlic oil and onion oil are responsible for the effects, as well as to determine the molecular mechanisms responsible for the anti-obesity and hypolipidemic activities,” they concluded.
Source: Nutrition & Metabolism
Anti-obesity and Hypolipidemic effects of garlic oil and onion oil in rats fed a high-fat diet
Published online 2018 Jun 20. doi: 10.1186/s12986-018-0275-x
Authors: Chao Yang, Lihua Li, Ligang Yang, Hui Lu, Shaokang Wang, Guiju Sun