Although olive oil, lemon juice and water are all relatively healthy, there isn't a lot of evidence to show that this combination improves your digestion. Each of these ingredients may have some benefits for your digestive tract, however.
Olive Oil and Digestion
Olive oil may help limit a type of bacteria in your digestive tract that's associated with ulcers, according to a study published in the Journal of Agricultural and Food Chemistry in February 2007. Virgin olive oil may even help to kill some strains of antibiotic-resistant bacteria.
An article published in Fats and Oils in 2004 noted that diets rich in olive oil help to limit stomach acid and trigger the release of a hormone that improves protein and fat digestion, making it potentially beneficial for people with digestive conditions.
Lemon Juice and Digestion
Lemon juice helps get your saliva flowing, starting off the digestive process. The main benefit of lemon juice in water, however, is that it has fewer calories than many other beverages, since each ounce of lemon juice has just 8 calories.
Proponents of drinking lemon juice in water claim that the acidity helps stimulate your stomach juices and limit any increases in blood sugar caused by your meal. The evidence is very limited to back up these claims, however, according to dietitian Toby Amidor in an article published on the Food Network website in March 2013.
If you suffer from acid reflux, you may want to avoid lemon juice -- it makes symptoms worse in some people with this condition.
Water and Digestion
While you don't need to drink water with meals to properly digest your food, liquids can help make it easier to swallow your food and help limit issues with constipation. Getting sufficient amounts of water or other liquids in your diet will help keep your stools soft and encourage your waste to move through your digestive system properly. Drinking plenty of water right before meals may help you fill up your stomach so you eat less during your meal.
Effects of the Combination
The lemon juice makes the combination of water and olive oil a bit more palatable, and the olive oil may counteract the acidity of the lemon juice a bit. Water also dilutes the acidity in the lemon juice, which makes it less damaging for your teeth.
There's no need to drink this combination to improve your digestion, though. Just include citrus fruits and olive oil as part of a healthy, balanced diet, and drink plenty of water, with or without lemon, to get the potential benefits from these ingredients.