There is an old saying that "it is better to eat ginger in the morning than in the evening." which suggests that different food taken during different times of the day might have different effects.

The daily variations in circulating fatty acid (FA) contents and lipid metabolism such as fatty acid oxidation, lipid uptake and transportation have been well documented. However, no reports yet have shown the daily rhythms of long chain polyunsaturated fatty acids (PUFA) in plasma and liver and expression rhythms of genes involved in de novo synthesis of PUFA in liver. It has been clearly proved that long chain PUFA play a critical role in preventing the development of metabolic syndromes such as obesity, insulin resistance and cardiovascular diseases. Thus understanding the daily variations of PUFA would be helpful in devising methods to prevent these diseases.

A team of researchers from the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) studied the daily pattern of PUFA contents and expression of genes related to de novo synthesis of long chain PUFA, with a pig model. The researchers collected blood and liver samples in a day at 3: 00 a.m., 7: 00 a.m., 11: 00 a.m., 15: 00 p.m., 19: 00 p.m., 23: 00 p.m., respectively.

The researchers found that long chain PUFA contents in plasma and liver both exhibited diurnal rhythms and they were higher at night than in the day. In addition, daily variations were also observed in gene expression of FASD1 (Delta 5-desaturase), FASD2 (Delta 6-desaturase), ELOVL5 (fatty acid elongase 5) and ELOVL2 in liver. Unexpectedly, these four genes encode the key enzymes involved in de novo synthesis of PUFA also exhibited a high expression at night. Moreover, they also noticed a similarity between the diurnal rhythms of these four genes and the circadian gene Period 2, which indicated that de novo synthesis of PUFA might be regulated by Period 2. "Our findings suggested that an intake of long chain PUFA in the morning, when they are relatively lower in plasma and liver during the day, might be more helpful for the prevention of the development of metabolic syndromes."said ZHOU Xihong, an assistant researcher at ISA.

This work was supported by National Key Research and Development Program of China (2016YFD0500504).

The study entitled "Diurnal variations in polyunsaturated fatty acid contents and expression of genes involved in their de novo synthesis in pigs"has been published in Volume 483, Issue 1, January 2017 of Biochemical and Biophysical Research Communications, details could be found at http://www.sciencedirect.com/science/article/pii/S0006291X16321866.