Yea, the whole point of the digestive process is to absorb fat, sugars, amino acids, etc from what you eat. Your body deploys insulin to regulate blood sugar that is absorbed in this process. Fiber provides protection in your stomach and intestine lining by moderating the absorption of glucose, preventing blood glucose spikes and regulating the deployment of insulin. Blood glucose spikes prevent your body from using fat for energy efficiently and synthesizing proteins. Saying that fiber is useless is a little disingenuous and innacurate since your body can't actually build muscle efficiently without it regulating how much insulin is deployed, no?