What Dr. Berg recommends as the number one source of fattening yourself up quickly, and correctly, is macadamia nuts. From my own personal experience, that seems to also be the case. Along your normal meal(s) per day, if you eat at least a 10 oz. bag of macadamia nuts in addition, you will gain multiple pounds per day due to the high fat content.
My dietary lifestyle is considered as low carb, with stabled blood glucose levels. I’ve learned to hate the dietary labels that are otherwise heavily misconceptualized.