The tot had suffered such severe weight loss his bones could be seen, Preston Crown Court heard.
Aleksandrs Vitte, 22, of Moor Street, Kirkham, fled to his native country of Latvia during court proceedings and was found guilty of the charge after a trial in his absence.
The baby’s mum, plant nursery worker Olga Karnopele, also 22 and of the same address, was charged with Vitte after health staff found they were failing to feed the tot properly.
She was jailed for two years, while Vitte received 32 months in his absence.
The couple discharged him from hospital against medical advice, promising to supplement his feeds, but did not, and he continued to lose weight.
Judge James Adkin said: “This case concerns serious cruelty to a newborn child.
“Records reveal he lost 250g in a week, his condition was evidenced by photographs. He was emaciated, in distress and he was quite literally starving
“A police protection order was immediately sought by doctors.
“You had been told your breastfeeding had to be supplemented with formula . But you ignored that agreement, you stubbornly believing that you knew best.
“You must have known and deliberately ignored the fact he was not thriving.
“Had the consultant not intervened and sought an order, and had you continued in the manner you had, he would almost certainly have died.
“You ignored advice from professionals and you breached agreements with doctors and removed that child from hospital when he was very poorly indeed.”
Karnopele, who pleaded guilty to neglect, had referred to formula milk as “poisonous” after concerns were raised by health visitors about his weight, and they saw she had no sterilising equipment in the house.
The baby, who weighed 6lb at birth, is said to have lost almost a quarter of his weight after he was born last November.
Karnoplele, a pale petite blonde, sat with a Russian interpreter in the dock as Richard Archer, prosecuting, said: “He was within the normal range for birth weight but a little over a month later on December 30 he weighed just below his 4.98lb
“It had been established he had lost more than 20 per cent of his birth weight.
“The bones around his chest were visible he was described as being lethargic and looking jaundiced and it is clear the photographs tell their own tale, he had lost fat from his face, arms and thighs and appeared to be very hungry.
“The doctor’s assessment was it was due to an inadequate intake of milk.
“He was admitted to hospital and given formula feeds and his weight gained rapidly.
“In January his weight had increased by half a kilo in a week and it was clear there was nothing medically wrong with him that stopped him gaining weight.”
The baby was taken to hospital on December 15 and the couple took him from the ward against medical advice, and agreed to supplement his feeds. But they made no attempts to bottle feed him.
By December 30, a midwife found him to be “pale and scraggy” and he was taken by ambulance to hospital.
Despite being told the seriousness of his condition his parents refused to let him stay at hospital, resulting in him being taken into care.
Karnopele cried in the dock as defending, James Heyworth described their conduct as an “inexplicable stubbornness”.
He added: “There is a degree of human tragedy for whatever the reason for their conduct, 10 years from now they may go on to regret the fact that not only did they fail him, they will never know him and the little boy will never know them.
“They will have to go through life wondering why they did not do right by him. The punitive consequences of her failures are all too clear.”