sure, you might not be fat but dirty calories (high saturated fats, additive, colourings, flavours and salt/sugar) can really fuck you up long term, colourings and flavours specifically can lead to cancer sure they may be deemed safe by FDA or whatever your government says but its impossible that every single one has been investigated thoroughly, remember they used to think asbestos was safe, and smoking, it was decades until they found it wasn't. Same can go for food additives. Long term studies will never be available until some damage has already been done. Saturated fat (which KFC is extremely high in) will raise LDL cholesterol increasing stroke and heart disease risk. no more than 5-6% of daily calories should come from saturated fats. High intake of salt raises sodium levels which will cause high blood pressure, osteoporosis, cardiac hypertrophy, stomach cancer, and kidney issues. you should eat no more than 6 grams salt a day as an adult and a single KFC meal alone contains well over 10g and you are for sure getting more salt throughout the rest of the day from other food Honestly you are only treating your body marginally better than a fatty and it will come back to bite your arse one day, maybe next year, maybe decades later. You become accustomed to these high salt, fat and sugar tastes in processed food, try take a break and only eat fresh food for 2 months, you'll go back and find that sugar is 4x sweeter than you realised before and its far to strong to deal with and you'll find that fatty chips feel terrible in your mouth. My rule of thumb is only buy from the first two aisles of the grocery store (fresh produce and meat) everything else is junk TLDR: you can be skinny and still incredibly unhealthy and at high risk of other health issues because of shitty ingredients in your calories. EDIT: you should get your bloods comprehensively checked at the doctors and you might be surprised how out of whack your values might be.