Let me dive right into it.
- Your app needs to have a good onboarding. You say about a Thousand users are visiting the app. However, they are not users, yet. Since you haven't explained the concept of your app to them yet. Adopt an intuitive way to introduce the new visitors to your app. As of now, you have a visitor who visits your page, doesn't know what's going on, why is it entering food items in the search box - leaves the web page.
GreenLane.io provides the perfect branding and experience to immediately register in the user's mind and not make him go back until he tries something.
- Your app is named Spelt, which about 90% of users relate to as an app that is somewhat related to correct spelling or pronunciation. I assume you've used the name because Spelt also refers to a type of Wheat (I hope). But that really doesn't help. Users generally do not wait for more than 3 seconds on a web page if they do not understand the content and/or are confused. You're following an amazing minimalist design of wonderful contrast and typography, but you are failing to convey what the app does. You could probably use colors which suggest it's related to Food such as Red or Green.
Consider Waqi.info's way of describing their acronym and specifying it in the title after you visit the webpage to know exactly what it does.
3. Positioning - The button placement is horrible. Considering I am not given a proper onboarding, the first thing I search for is the "How it Works" or "About" page of the app, which is not visible at all, at the bottom.
4. Advantages - Your application does a wonderful job of measuring food items. Use that to your advantage and possibly state facts, in text below the calculator box, which are random. Such as, "Ounce by ounce, Nutritious food costs up to 10 times more than junk food!" This all will contribute to the overall branding of your application and will reduce the bounce rate when the visitor will use the application.
5. Why will they come back? - To reduce the bounce rate, it's important to have a feature or experience which will get the user to visit you again. For example, you could have a cookie store the data of the user in his machine which you'd be able to fetch and welcome him. Also, the possibilities of how many exercises you'll need to do to slash those calories you're considering to eat. Example: For a Slice of Pizza, say 32 minutes of Cardio and 20 Reps Crunches.