What deficiency is it for lumps under new nail growth

Nail fungal infection

You may have a nail fungal infection — also called onychomycosis (on-i-ko-mi-KO-sis) — if one or more of your nails are:

• Thickened
• Brittle, crumbly or ragged
• Distorted in shape
• Dull, with no luster or shine
• A dark color, caused by debris building up under your nail

Infected nails may also separate from the nail bed, a condition called onycholysis. You may even feel pain in your toes or fingertips and detect a slightly foul odor.  However, all may not apply in your situation.

Click Here to Find Causes for the Problem

Click Here to Know When to Seek Medical Advice, Also a Prevention and Self-Care Link 

I have not found any reference to diet.  Perhaps all of the above does not answer your question and seeking the advice of a doctor may be best.

My regards 

The state of your nails reflects exactly the state of your body. I think that you need to be consulted by a medical staff (with a blood test also).

But what you can do is a nail bath of 36 -37oC with sea salt in water.

Thake this bath for 5-7 min when ever you can. It helps strengthen nail.

It can be a sign of a deficiency of either zinc, magnesium or calcium or all three! You need to take these supplements for at least 3 month to see effect.