Trichologist Anabel Kingsley, daughter of the late "celebrity hair doctor" Philip Kingsley, has spent years studying the hair and scalp.
Currently based at the family's world renowned clinic in Mayfair, London, she recently spoke out about her own experience of hair loss that she suffered following the death of her father in 2016.
Kingsley told Business Insider that she is seeing more and more cases of hair loss at her clinic, particularly among young women. The reasons for this, according to Kingsley? The rise of the fad diet, as well as the sharp increase in popularity of veganism and vegetarianism.
'Hair thinning' is a gradual reduction in volume
There are two types of hair loss, according to Kingsley.
The first is a gradual reduction in volume, otherwise known as "hair thinning." This is more common in older women but can also occur in young women as part of a genetic predisposition to follicle sensitivity.
This means that the hair follicles on your scalp are overly sensitive to normal levels of male hormones. "If you're experiencing thinning it doesn't mean you have more hormones than you should, just that you're more sensitive to them," she said.
"It's hard to say whether more women are losing their hair or just that more are speaking out about it, as it's now less of a taboo subject. With it being in the press more and more, women have the confidence to speak out."
Nutritional deficiency can cause 'reactive hair loss'
It's the second type of hair loss, called telogen effluvium, that Kingsley thinks is on the rise, particularly among women.
Telogen effluvium is a reactive hair loss which leads to excessive shedding, she explained, and can be the result of stress, being unwell, having a fever, or of a nutritional deficiency.
And Kingsley points to the rise of the fad diet and, in particular, the popularity of veganism and vegetarianism for the latter.
"Diets can be helpful if you're incredibly mindful, but often people aren't," she said. "Hair is not an essential tissue, meaning the body can physically survive without it, even if you are really careful it can be hard to get the protein and iron for hair to grow healthily.
"If you're not eating enough of the correct foods or your body is not absorbing enough of the nutrients, this can result in excessive shredding," she said. "Even if you're only slightly deficient in a nutrient, the body withholds this from the hair first."
She added that her clients seeking specialist help for this type of hair loss often appear fit and healthy in all other respects.
While she has also seen more cases of crash dieting, restrictive eating, and unbalanced vegan and vegetarian diets causing telogen effluvium in men in recent years, they are less likely to be iron and ferritin (stored iron) deficientthan women as they do not menstruate — and these deficiencies are common causes of hair loss.
Vegan and veggie diets don't give the hair what it needs
"I can completely understand my clients' reasons for being vegan or veggie, but it's very difficult with those diets to combine the correct food groups to give the hair what it needs," Kingsley said.
"For example, fish and eggs have all eight essential amino acids (proteins) that you need, while a grain or legume would only have a few of those. If you only get one set from a source of protein you need to get the rest from something else."
Kingsley advises her vegan and vegetarian clients to up their protein intake and look up the different components of each protein to make sure they are getting all the amino acids they need. "We also recommend they take a vegan-friendly protein supplement," she added.
"Your body can make most amino acids on its own, but eight of them (called essential amino acids), it cannot. They therefore have to be consumed daily."
Getting enough iron is key — even in supplement form
For those of us thinking we're getting enough iron from leafy greens, that might not be the case.
It's more difficlut to absorb sufficient iron from plant-based sources (non-heme iron) compared to, for example, red meat (heme iron).
"Iron is really, really important, particularly for women who are menstruating," Kingsley said. "And the iron in dark leafy greens like spinach and kale is actually very difficult for the body to absorb — you might only be getting about 3% of it."
She generally recommends taking iron supplements — the slow releasing type are usually better, she says, as they don't cause as many side effects. However, they must be combined with vitamin C, as without that the body cannot absorb the iron.
"Our vegan supplement called Tricho Complex also contains B12, that's absolutely essential for vegans and vegetarians," Kingsley said.
Finding a B12 source is important for vegans because it's mainly found in animal products.
"The body stores B12 for three years so you might not notice a deficiency straight away, but it will happen if you don't get it from other sources."
Kingsley added that if you've dramatically changed your diet or been unwell and it has sent hairs into the "telegen phase" you won't see excessive hair fall immediately — instead, you'll notice it up to three months later.
"If you feel like you're losing too much hair, you need to think back to what you were doing/eating [a few months earlier]," she said. "Did you have a fever, were you on a juice fast?
"It can be quite comforting for my clients just knowing that there's a a definitive reason why they have been losing hair."
Although Kingsley is not the first to suggest a link between cutting out meat and dairy with hair loss, there is a lack of conclusive research into the field.
An article published in the NCBI, said that "while iron deficiency (ID) is the world's most common nutritional deficiency and a well-known cause of hair loss, it remains unclear what degree of ID may contribute to hair loss."
It added that "vegans and vegetarians are also at higher risk for ID, as their requirements for dietary iron are considered to be 1.8 times higher than for meat consumers. It may also be the result of a reduction of storage iron, measured by serum ferritin.
"Although multiple studies have been conducted, it is unknown if a deficiency of storage iron contributes to hair loss, as conflicting results have been noted," it went on.