Whole-grain foods contain many nutrients as well as fiber that helps to slow your digestion and slowly releases energy so you will not end up with high sugar spikes after eating them. This will keep your insulin levels low as well, and the glucose you take in will be distributed to your cells properly so you have the energy to burn up quickly.
When you take in simple carbs that contain sugar and white flour which are the foods described above, the energy is released too fast. This stresses your pancreas and you end up releasing a lot of insulin as well which makes you tired. You do not end up using a lot of energy either as it is not distributed properly. Therefore, the energy becomes stored in your fat which contributes to weight gain. Your arms will not be toned this way.
Therefore, you want to replace your simple carbs or starches made with sugar and white flour with whole-grains. Whole-grains include oats, spelt, sorghum, quinoa, barley, and buckwheat. Therefore, when you want to grab a loaf of bread, for example, choose bread made of any type of whole-grain.