Yes you must finish all the sachets , the contents are carefully balanced to ensure maximum weight loss whilst delivering all the vitamins and minerals your body needs . Other than being harmful to your health , only having 2 sachets could slow down your weight loss . The calories in the shakes is the minimun you need without your body going into 'starvation mode ' where it wil stop burning fat and start burning muscle which is more efficient .. but you dont want to loose muscle .. and remeber your heart is a muscle .....