Lemon water may help with weight loss.  

Lemon

Lemons are often promoted as a magical weight loss food that will help the drinker lose weight with no addition of any other activities or changes to your diet.  It sounds like a bridge too far.  I discussed lemons water and the research behind it over a year ago.  There are a few theories as to why lemons may help with weight loss, and we will discuss them and whether they are true.  

One common theory is that lemon juice contains soluble pectin fiber and it expands in your stomach thus helping you feel full for longer.  Another theory is that flavonoids boost your metabolism and thus cause you to gain more weight.  The problem with these two theories is that these items are contained in the whole lemon and juicing or squeezing prevents them from being added to the water in a measurable amount.  Few people eat lemons whole, and because of this, it is highly unlikely that lemon juice which contains very limited pectin or flavinoids could be responsible for a measurable degree of fullness or caloric burn.

Another theory is that lemon water alkalinizes your body and flush away toxins.  Flushing away toxins creates a boost in your metabolism and thus burns more calories.  First, detoxification burns calories so helping the body do this would reduce calories burned.  Second, the pH of your blood and cells cannot be altered by what you eat, but most important, lemon juice is an acid so alkalinization would not occur.  And though water is a key component of your body’s detoxification processes, there’s no evidence that adding lemon improves the process.

So what does the research show?  

1. Drinking water creates a thermogenic effect.  If lemon juice increases water consumption, it could help by ensuring you drink enough water to create the effect.  A study from 2003 showed that 2 liters of water increased caloric expenditure by just under 100 calories[1].  This finding was confirmed by at least one additional study[2].
2. Water promotes satiety.  I already reviewed several pieces of research on water and satiety.

The bottom line:  Water can promote fullness and support hydration.  It may even boost metabolism and assist with weight loss more when lemon is added, but a quality research project has not been completed.  I suspect that lemon water is no better than regular water when it comes to losing fat.  If it helps you lose weight and you like the flavor, bottoms up because it can be used as a low-calorie replacement for higher-calorie beverages.