You may need to skip the cake, or at least limit your intake of sweets and carb-heavy vegetables. Know your body and do what makes you feel best. If you don’t think you will be able to get back on the Keto Diet comfortably after having a “cheat day” or “cheat vacation,” then perhaps it might be best to continue eating a strictly Keto-friendly diet.
To figure out the correct amount of fiber for your body, try experimenting. If you’re on the keto diet, start with 15-20 grams of total dietary fiber per day from a mix of soluble and insoluble fiber for several weeks, then consider adding 3-5 grams at a time as needed to see how you feel. Remember that some people actually feel worse when they boost their fiber intake[*][*][*].
One study compared the glycemic response of SCF to the glycemic response of glucose in 12 healthy adults during a randomized, controlled, crossover study.[6] The findings of this study revealed that SCF had a significantly lower incremental glucose and insulin response than that of the glucose control. Additionally, another study observed a significant lowering effect on postprandial (during or after food consumption) blood glucose and insulin (coinciding with an increase in fat oxidation) upon consumption of 55 grams of SCF in 18 overweight adults, compared to a full calorie control.
Going on vacation is exciting, until you realize you just started the Keto diet. When you’re headed on vacation, believe it or not, but there are tons of ways you can stick to the Keto diet. Many people would agree when someone says that Keto is a way of life and not just a diet. Before you start on your vacation, you’ll need to keep this in mind. Don’t stress about eating keto when you are on vacation, it is fairly easy to keto on vacation! 
Skimping on fiber isn’t good for your digestive health, as it feeds the good bacteria in your GI tract, something that benefits you beyond adequate bowel movements. “The digestive tract is where your body’s second brain is, and it’s home to the majority of your immune system,” says Elia. “If you’re following keto, it should be one of your biggest priorities to make sure you get adequate fiber to keep your gut healthy and happy,” she adds. And, she notes, high-fat diets slow digestion and decrease GI motility, so it’s especially important to get enough.