Skincare Shots: Edible (and drinkable) collagen is hot in Japan. Photo: Rebecca Milner

Marshmallows, cheesecake, soups and soft drinks that promise firmer skin? Welcome to Japan!

Collagen has long been applied from the outside in for fuller, younger looking skin. But in the past few years the Japanese have been hoping it can work the other way around. There, legions of women are eating and drinking the protein in hopes of achieving a skin plumping effects.

First came the supplement drinks -- petite vials of collagen-rich liquid meant to be swallowed along with breakfast. One of the original varieties, Fracora 500 (created by Kowa), packs in 10,000mg of fish collagen in a single serving and has sold a mind-boggling 55,000,000 bottles since its 2004 debut.

Shiseido has a popular version too, called The Collagen. All of the above are sold at the local drug store or online in individual bottles (for an extra boost) or in cases for daily consumption. At roughly $3 a serving, it's not much more than your daily latte.

Shiseido's collagen kits, sold at Natural Lawson, a Japanese convenience store. Photo: Rebecca Milner

But what if you could get your latte and your collagen in one? This was the line of thinking that led to the current mania in Japan for "collagen enhanced" food.

Supermarket and convenience store shelves have become stocked with everything from juices and yogurt drinks to marshmallows and cheesecake spiked with the precious (though questionably effective) stuff.

But despite many health and beauty experts stepping in to debunk the benefit claims, the mania continues. Why? "Why not?," is the typical response, just so long as it doesn't do any harm. After all, you were going to reach for those marshmallows anyway, so why not feel like they might have a positive effect?

Collagen enhanced candy at Natural Lawson, a Japanese convenience store. Photo: Rebecca Milner

Restaurants, meanwhile, have turned the trend into a meal.

A quick search on GuruNavi (a Japanese online restaurant guide, the name is short for "gourmet navigation) turns up over two dozen collagen-themed restaurants in Tokyo. Most are located in fashionable districts like Ginza, Roppongi, and Nakameguro.

Harunohi, a collagen restaurant that has now grown to chain status, features a "beauty" lunch set (for under $10). Along with a plate of fresh udon noodles topped with steamed farm fresh vegetable and a soft boiled egg, the main dish is a piping hot bowl of collagen soup. The women flocking to these stylish joints aren't just sucking it up in the name of beauty-the rich, salty broth goes down like a hearty chicken soup on a cold day.

With winter around the corner, restaurants are gearing up to do brisk business in collagen hotpot stews with chunks of pork and chicken. Pigs feet, a traditional delicacy of the Okinawan islands, has likewise come into otherwise unexpected vogue.

The "beauty lunch," a collagen-enhanced meal at Tokyo collagen-focused chain Harenohi. Photo: Rebecca Milner

The blogosphere has responded to the trend with do-it-yourself collagen recipes from amateurs and celebrity cooks alike.

Want to know how to make that collagen cheesecake yourself? (Here's the spoiler: just add a packet of dried collagen powder to your standard recipe.) On that note, however, the whole fad starts to make sense -- it beauty advice that makes us feel good about our food and actually encourages us to eat more cheesecake.

- By Rebecca Milner

Rebecca Milner is an American journalist and trendspotter living in Tokyo. She reports for StyleList on beauty, fashion and style trends in Japan.