This invention is a wearable device to measure a person's consumption of selected types of food, ingredients, or nutrients comprising: a housing that is configured to be worn on the person's wrist, arm, hand, or finger； a spectroscopy sensor that collects data concerning light energy reflected from the person's body and/or absorbed by the person's body, wherein this data is used to measure the person's consumption of selected types of food, ingredients, or nutrients； a data processing unit； and a power source. The selected types of food, ingredients, or nutrients can be selected from the group consisting of: food that is high in simple carbohydrates； food that is high in simple sugars； food that is high in saturated or trans fat； fried food； food that is high in Low Density Lipoprotein (LDL)； and food that is high in sodium.
