Many people are broken. They have faulty glucose metabolism, a sluggish liver and pancreas, irritated bowels, bacterial overgrowth- any number of acquired conditions which mostly stem from poor diet and lifestyle. This puts the body in such a state where it cannot properly assimilate the things it needs from good, healthy foods, or it may even be rejecting things that would otherwise be very good for your constitution.
The answer is not to start downing supplements. A health-building diet and lifestyle is both about adding things that are beneficial/health-restoring (exercise, proper food, sun & vit D, adequate rest, perhaps some targeted supplementation) as well as removing barriers to optimal health- whatever is standing in the way of your body healing and optimizing its own function. This could be your binge drinking several nights a week. Or your inability to say "no" to the franken-fried chips and french fries in front of you. Even eating certain "healthy" foods place large burdens on your system. Maybe you never get up off your butt and move your body, or don't sleep enough, or you sleep too much.
I often see references to obscure tribes or groups around the world that eat extreme diets, such as the Inuit or various Pacific Islanders. Some eat 70% starchy carbs from sweet potatoes, others eat nothing but meat, milk and fat. One group gets 50% of calories as saturated fat from coconut. These people thrive and flourish on their whole-food diets regardless of macronutrient ratios, and are virtually free of disease. Take these people out of their environment, and place them in a Western diet/lifestyle- BAM they get diabetes, heart disease, cancers.
Bottom line- breaking your body with processed, refined carbs and sugars, industrially manufactured vegetable oils, drugs, booze, sitting on your ass all day in front of a TV etc absolutely will cause disease. This is exactly why you need a multi-faceted and holistic approach when looking to build health and create life-long habits that will contribute to your wellbeing.