FRUIT COMBINING
I love fruit. It’s a staple in my diet no matter the time of year (nothing is quite as satisfying as some watermelon slices in the heat of summer) and something I consistently try and get more and more of. Though the USDA recommends two servings of fruit per day, there are many other systems of belief that lean more towards 4-5+ (this is what I personally aim for!). Sometimes these recommendations are difficult to meet, but it can be achieved by adding berries/banana to some oatmeal, having a fruit smoothie, or even something sweet - like peaches - as dessert. As much as these ways of implementing fruit into one’s diet is amazing, there is some research behind it not being the most optimal for digestion.
Disclaimer*: the following is a (research backed) opinion and should not deter anyone from consuming fruit when and how desire. Something is always better than nothing when it comes to fruit!
Given how quickly fruits travel through the digestive system, it is recommended for optimal health/digestion to eat fruit before - and not with - other foods. Fruit, in combination with other food, can stick in the digestive system along with the slower digesting foods (protein and starches) and begin to ferment and disrupt digestion in the gut. This is a nightmare for your tummy and can quickly lead to gas, bloating, and other uncomfortable effects.
Fruit is split up into 4 groups: acidic, sub acidic, sweet, and melon. As shown in the diagram below, sweet fruits and acidic fruits are not the best match but both do OK with sub-acidic fruits. It’s recommended melons be eaten by themselves, as they don't combine well with any other fruit or food given their quick (~10min!!) rate of digestion.
If attempting to be more mindful about fruit combining, aim to have fruit about 30min to one hour before a meal or two hours after to allow for proper digestion of all food.
In regards to smoothies, there are definitely different lanes of thought. For example, when I make a smoothie with mixed berries and banana (acid + sweet) I notice more of a tendency for an upset tummy opposed to if I use fruit within the same family. Additionally, with smoothies in particular, be mindful of just how much food has been blended into a drink. It’s tempting to guzzle down a smoothie since it’s so quick and yummy, but it’s unlikely one would eat a banana, handful of berries, peanut butter, a couple cups of greens, and nuts within a few minutes. As with everything, trial and error and see what works best for you and your body!