Previous laboratory studies of animals (including rats, fruit flies, worms and mice) have shown those fed a calorie-restricted diet may live up to twice as long as those with an unrestricted diet.
Now US researchers at Yale University, whose study was published in the journal Science, have reported moderate calorie restriction (14%) may benefit human health – as well as identifying a key protein which might increase ‘health span’ (the number of disease-free years a person lives).
A calorie-restricted diet involves small reductions of habitual calorie intake over a long period. In this study over 2 years, the scientists assessed 200 participants aged 21-50 who had a body mass index between 22.0-27.9 (putting them in the healthy, non-obese category).
The researchers specifically looked at the effect of calorie restriction on the thymus – a gland situated in the chest (just above the heart) which is part of the immune system and produces T cells (white blood cells essential for fighting infections).
Hormones released by the thymus inhibit the ageing process; but as humans age, their thymus becomes fatty and smaller, producing fewer T cells. Hence, older people are more susceptible to infections due to reduced immunity.
When the scientists performed MRI scans of participants’ thymus glands, they found those with calorie-restricted diets: had greater functional thymus volume than those with unchanged diets; and their thymus glands were less fatty and produced more T cells.
In addition, while the thymus was being ‘rejuvenated’, there were no changes to the immune cells the gland was producing.
The team then also examined body fat (adipose tissue) – key to the functioning of the immune system – because some immune cells in this tissue can cause inflammatory responses when wrongly activated.
They found the gene PLA2G7 (a protein produced by immune cells called macrophages) was causing the effects of calorie restriction.
Study senior author Professor Vishwa Deep Dixit told medicalnewstoday.com: ‘These findings demonstrate PLA2G7 is one of the drivers of the effects of calorie restriction.
‘Identifying these drivers helps us understand how the metabolic system and the immune system talk to each other, which can point us to potential targets that can improve immune function, reduce inflammation and potentially even enhance healthy lifespan.’
Professor Dixit also noted that, as restricting calories can be harmful to some people, manipulating PLA2G7 ‘might provide benefits without the need for restriction’.
