Nicola McKay from Greenock has shed a massive six stone since last October and determined Tiffany Broadfoot from Wemyss Bay has dropped four stone and four pounds in just 17 weeks.
The pair, who are both 20, say they are feeling healthier and that their confidence levels have soared following their dramatic transformations.
They are now determined to keep the pounds off and continue losing weight until they reach their ideal target.
The girls have been following a healthy eating plan devised by Michelle Phillips of Weightwise Health and Fitness.
Tiffany, who works at CalMac, told the Telegraph: "My life has changed completely - I spend most of my free time at the gym and I am determined to keep losing weight to meet my target."
Nicola added: "Before, I would drink fizzy juice during the day and eat junk food.
"But now I watch what I'm eating and drink water during the day - I feel so much better about myself and much healthier.
"People are telling me that I look like half the person I was before."
Tiffany's dramatic weight loss is also attracting positive comments.
She said: "People have noticed the difference - it is nice to hear."
To mark their achievements, Weightwise owner Michelle, from Gourock, who runs classes across Inverclyde, has presented the girls with awards plus £50 in cash.
Michelle said both girls had driven down their body mass index, or BMI, to much healthier levels with Nicola's falling by 12.1 and Tiffany's dropping 8.9.
She added: "I am so proud of Tiffany and Nicola, they have shown great determination to lose this weight.
"I think that it is an especially great achievement given their age, as they have resisted the temptations that come with being 20 - such as going out with friends and drinking cocktails.
"I'm confident that Tiffany and Nicola will keep up their new healthy lifestyles as they grow older."