When used to understand nutrition, "calories in equals calories out" is the message of the First Law Of Thermodynamics. Everything on Earth, including horses, abides by this law; however, many factors affect both sides of the equation. It makes sense because every horse responds differently to the foods eaten and the amount of work done. Identifying the factors affecting a horse's response to what they are fed starts with understanding this law. I offer the vision of "adjusting the dials" when feeding individual horses, but this concept is lost in modern technology. Computers automatically adjust factors in engineering, such as automobiles. However, when feeding horses, what kind and how much going in will be balanced with their overall health by systems within the horse. Adjusting the food and its associated inflammatory factors will positively or negatively affect these systems. It is one example of the many "factors" affecting both sides of the "calories in equals calories out" equation. Helping to understand this complex concept, I use a simple banking analogy called the balance sheet: money in versus money out. Having too little makes painful problems, but having too much can too. Balancing the stress of taxes and excess work associated with more income offsets the extra work involved in maintaining what the money buys. To this point, horse owners work harder and longer to create the extra cash for the care of horses (or eat more food to build body fat reserves), while enjoying the use of the horse requires time and energy in training and competing (diet and exercise to maintain the ideal weight). Adding the work needed to keep both sides close to balance is a lifelong challenge for all things, including our horses. The better we do this, the healthier our horses will be.