She said she "nearly died" seeing herself so chubby, in a caption accompanying the photo.
Tay also said from a young age she "swore" she would find the best slimming method and jubilantly ended the post saying that she has "made it!"
Most comments, however, were far from encouraging.
Many commented that she looked great at 16 and was far from fat, criticising her to be "contented with what she has".
One said: "Come on. That is not call fat. Even if you insist that you are "fat", it is also nothing wrong to be fat. When a woman gets older, its better to be a bit chubby and fatter, than thin and bony. Healthy is the word. It is not a question of fat and skinny."
The actress later clarified in a later comment that her "fat" post was based on not just weight, but body fat percentages and visceral fat levels.
"Many said i was not fat then, and now is too skinny. Harlow... r u me? U know how much i weigh now? According to HPB, the National Health Survey 2010 stated that 60% of Singaporeans are overweight.
"I have been giving health talks for HPB the last two years and I know it too well that I am having a perfect weight now at 54kg with healthy body fat at 22%.
"When I was 16 I was 67kg and overfat.
"Hence, am I too skinny now or are you guys wrongly taking chubby as healthy?
"Overweight is not healthy as it posts a risk for diseases. I would suggest all chubby people go take their body composition readings, not just of the weight, but also their body fat % and visceral fat level.
"Then they will know if they are really chubbily healthy or totally unhealthy.
"Its time that our 60% of the overweight Singaporeans go on a healthy, balanced diet and start to exercise!"