My personal low carb diet starter guide:
Oats may not be completely bad for keto, but the only problem lies in its carb content of oatmeal. Since oatmeal is derived from the whole-grain content, it constitutes a good portion of carbs. As already mentioned, a 100-gram serving of oatmeal will have 66 grams of carbs, including 55 grams of net carbs.
Plain, instant oatmeal is slightly lower in carbs, with 27 total grams and 23 net grams. Flavored oatmeal can be higher in carbs due to the addition of sugar and fruit.
There Is no doubt that low carb diets work very well in the short-term to reduce weight, primarily by cutting the calories and improving satiety. However, consuming high fat diets for a long period is sure to cause adverse effects that negate the acquired weight loss benefits.