High protein intake is harmful to your kidneys.
There is no conclusive evidence that this is the case. The usual recommendation is to eat your target body weight in grams of protein daily. For example, if you're 180-lbs but want to be 200-lbs, eat 200 grams of protein daily.
Sweet potatoes are better for you than white potatoes.
The reality is that both types of potatoes have complimentary nutritional differences but one is not necessarily better than the other. For instance, sweet potatoes have more fiber and vitamin A, but white potatoes are higher in iron, magnesium and potassium.
Red meat causes cancer.
No study has shown a direct cause-and-effect relationship between red-meat consumption and cancer. How the meat is cooked is really what is at issue here: overcooking meat under high heat tends to increase the release of carcinogenic compounds which increases cancer risk.
High-fructose corn syrup (HFCS) is more fattening than regular sugar.
Both HFCS and sucrose, or table sugar, contain comparable amounts of fructose. At issue here is not necessarily HFCS but fructose in general. Consuming either HFCS or sucrose will cause weight gain, in the form of fat, when consumed in excess.
Salt causes high blood pressure and should be avoided.
If you have a healthy blood pressure of less than 120/80, there is no need to restrict salt intake. On the other hand, if your blood pressure exceeds the aforementioned amount, it may be wise to cut down on your salt intake and increase your potassium intake. The reality here is not so much how much salt or potassium you eat, but rather the balance between the two minerals that matters most. Hence, if you eat a high-salt diet but very little in the way of potassium, then you should lessen the imbalance between the two minerals by either eating less salt or taking in more potassium. Good potassium sources include spinach, broccoli, bananas, white potatoes, and beans.
Brian Danley, CFT
"Motivation is what gets you started. Habit is what keeps you going."