The above statement contains an element of cliche.The treatment accorded by the Japanese to their captured prisoners -- American, British, Australian, Sikh, Chinese and Filipino -- was a bestial disgrace.
Japanese treatment of POWs and civilian prisoners varied from place to place, and over time. In general, it can be said that, apart from individual incidents of atrocity during the rapid advance at the end of 1941 and the beginning of 1942, the Japanese treatment of prisoners was reasonable at the beginning, and then gradually got worse, particularly in the last two years of the war. The essential factor causing that worsening of treatment was the supply crisis within the Japanese-occupied area resulting from the Allied interdiction of sea transport, meaning that rations were drastically curtailed to bare subsistence level.
The Australian prisoners of war may serve as an example. About one-third of them died, about the same mortality rate as that of German POWs in Soviet hands. Almost all these prisoners had been taken at the fall of Singapore, at the beginning of 1942. That means that some two-thirds survived about three and a half years of imprisonment in Japanese-held areas that were increasingly under siege.
The same consideration applies to other Allied POWs and civilian prisoners. The vast majority were captured at the beginning of the Japanese advance, and were held for several years; their survival rate therefore needs to be seen against the length of time of their captivity, and general conditions within Japanese-held areas.
A comparison may be made with German POWs in Soviet hands. As stated, their mortality rate was about the same as that of Australian prisoners of the Japanese. However, the pattern of mortality was quite different.
About half of the German POWs in Soviet hands were captured during the war, the great majority in the last year of the war; the other half went into captivity after the German surrender. Almost all of those captured in the first two years of the German-Soviet war died in captivity; for example, 90% of the Germans taken prisoner at Stalingrad died. Those taken prisoner in 1944 had a lower death rate, and those who went into captivity at the end of the war had a still lower death rate; but the German POWs continued to die in relatively high numbers even after the end of the war.
By contrast, in the case of the Australian POWs, the death rate was very low to begin with, and then got a lot higher as conditions worsened. Thus, Australians taken prisoner by the Japanese at the beginning of the Pacific war had a much higher chance of survival (over 60%) than Germans taken prisoner in the first two years of the German-Soviet war (less than 10%). I imagine that the pattern of mortality among other Allied prisoners was similar to that of the Australian POWs.
As I stated, the treatment of the prisoners also varied from place to place. While the Australian POWs held at the main POW camp at Changi, in Singapore, were more or less left to their own devices within the camp perimeter, and were thus able to grow their own food and institute other organisational measures to maximise their chances survival, those sent to work on the Burma-Siam railway suffered an appallingly high mortality rate from disease, due to a combination of poor diet, exposure to extreme climatic conditions (especially during the wet season), and harsh treatment dictated by the work tempo.
It is interesting that the single most common cause of death of Australian POWs in Japanese hands was attack by Allied forces on localities where they were held. Thus, the largest number to die in a single incident were those who perished when the ship taking them to Japan was torpedoed.
However, most died from exposure and a wide variety of diseases, exacerbated by malnutrition. Only a small number were actively killed by the Japanese, either individually or during sporadic massacres. The largest single massacre of Australian POWs occurred during the Sandakan "death march", at the very end of the war, when their Japanese guards were trying to escape the Allied forces which had landed in Borneo.
The case of the Indian POWsis also interesting. Although they suffered much the same conditions as other Allied prisoners, a substantial minority joined the Japanese, and fought with them against the British in Burma. It is those Indian POWs that are honoured in India today, rather than those who remained loyal to Britain.