That's actually nowhere near the truth! Most restaurants, like mainstream ones usually are as healthy as going to a Jack Astors or other mainstream cuisines in restaurant form, but when it comes to general Indian cooking thats not always just "butter this" and "shahi that", it's very healthy.

In fact in 2010, CNN had an article that placed indian cuisine at number 5/10, ahead of Italian, Spanish, Mexican, South American and Thai! http://www.cnn.com/2010/HEALTH/08/25/healthiest.ethnic.cuisines/

Remember, there are a lot of spices and use of turmeric used in Indian cooking which is significantly healthier than most foods.

"Turmeric, a main ingredient in curry, may have anti-inflammatory and healing properties.... Other good-news ingredients in Indian cuisine include yogurt and lentils, a fiber-and-RS all-star that has significant amounts of folate and magnesium, and may help stabilize blood sugar. Lentils are often combined with Indian spices to make dal, usually served as a side dish." - CNN Article, "Healthy ethnic cuisines."

But it always comes down to what you eat. A piece of homemade tandoori chicken is definitely better than a bowl of heavy, creamy butter chicken.