To start a keto diet, you will want to plan ahead. That means having a viable diet plan ready and waiting. What you eat depends on how fast you want to get into a ketogenic state (ketosis). The more restrictive you are on your carbohydrates (less than 25g net carbs per day), the faster you will enter ketosis.
You want to keep your carbohydrates limited, coming mostly from vegetables, nuts, and dairy. Don't eat any refined carbohydrates such as wheat (bread, pasta, cereals), starch (potatoes, beans, legumes) or fruit. The small exceptions to this are avocado, star fruit, and berries which can be consumed in moderation.
Do Not Eat
Grains - wheat, corn, rice, cereal, etc.
Sugar - honey, agave, maple syrup, etc.
Fruit - apples, bananas, oranges, etc.
Tubers - potato, yams, etc.
Do Eat
Meats - fish, beef, lamb, poultry, eggs, etc.
Leafy Greens - spinach, kale, etc.
Above ground vegetables - broccoli, cauliflower, etc.
High Fat Dairy - hard cheeses, high fat cream, butter, etc.
Nuts and seeds - macadamias, walnuts, sunflower seeds, etc.
Avocado and berries - raspberries, blackberries, and other low glycemic impact berries
Sweeteners - stevia, erythritol, monk fruit, and other low-carb sweeteners
Other fats - coconut oil, high-fat salad dressing, saturated fats, etc
