As the proverb says "you are what you eat" a diet has a tremendous impact on your well-being and your physical ability. Making a few changes to an unhealthy diet may significantly increase your performance. Let us take a look at it from a Muay Thai fighter perspective.
#1: Don't start a completely new dietary plan straight away.
It may be easier for you to introduce some changes to your training diet gradually. This way it won't feel like such a sacrifice and you will more likely stick with it. There is no point of forcing yourself to eat things which you don't like - healthy doesn't mean untasty. A healthy diet for training can be tasty once you give it a chance. The diet needs to be balanced but that doesn't mean that you cannot treat yourself from time to time - increased metabolism due to systematic training will take care of some extra calories. That said, there are certain products to avoid if you want to make a good progress. Let's take a look at a good Muay Thai diet. It has kept me in a good physical condition for many years.
#2 Consume all groups of foods.
The main "trick" lies in a proper balancing all of them and not avoiding some of them, like fats, and overeating some other like proteins. Just be sure that you consume quality fats, like virgin oil and avoid trans-fats. Good fats, in general, are beneficial for you since our bodies need fat to absorb protein and to maintain a hormonal balance. This reminds me of a funny story of my friend who is a bodybuilder and a very healthy man indeed. I never saw him sick in his entire adult life. Once he went for a very restrictive almost pure protein diet for a few weeks, eating cooked chicken and eggs and almost completely avoiding eating fat. What happened is that he deregulated his immune system and contacted a cold in a perfectly good, warm weather. So when someone tells you that fat is bad it is partially true: excessive intake of saturated and trans fat is bad and moderate consumption of mono-saturated fats is good for you. That's one of the reasons why it is so important to maintain a healthy, balanced diet and not a restrictive one. Even if you eat 5000/6000 quality calories and train like a devil an increased metabolism due to training will take care will take care of it and the increased muscle volume will burn it. Unless your metabolism rate is really very slow then don't listen to me and toss your green salad :-)
#3 Types of foods which are beneficial for your training:
Fruits and veggies, but there's a catch: some fruits like grapes and pears have a large quantity of fructose which not very good for, a healthy and sporty, you. Bananas are better since it has a low fructose levels and it is a good source of fiber (starch) Gelatin: if you don't get enough of it from your food you should consider supplements. Gelatin is great for your joints and makes your bones stronger which is a must with an intense training. I can't really recommend gummy bears for a gelatin supplements cause most of the products are just pure sugar bombs.
#4 Types of foods that are not recommended in a training diet:
Bad carbs like white bread (a whole wheat bread is better but contrary to the popular belief it is not some kind of a super food) and pasta, regular fried potatoes Sweets in most forms Overdosing alcohol (more about it at the end of this post)
#5 Schedule you means:
Eat regularly so your body is always powered and able to recover and rebuild after a regular training. The commons wisdom says that a breakfast is the most important meal, and that's true. Breakfast gives you a fuel for the rest of the day and it should be rich in carbs, proteins, and some quality fats. It is also wise to avoid heavy meals late and in the evening and have a rather modest supper. Have a light healthy snack before a training and let it digest before you start your workout. Banana or a nutrition bar (a carbohydrate bar, not a protein bar. Protein bar is better after workout). This will give you a fuel to have a longer and a more intensive training. A proper meal schedule is a cornerstone of an effective Muay Thai diet.
If you read my other posts then you know that I don't avoid controversial subjects. That's why I would like to talk about alcohol in your diet. Is it good, or is it bad to drink alcohol when you are training? The answer is: depends on how much alcohol you consume. Alcohol consumed in low doses after a workout may boost your blood testosterone levels and be beneficial for your training. But there a catch: a large amount of alcohol: interestingly enough, according to some studies, alcohol in low doses increase testosterone levels, but consumed regularly and in large doses decrease it significantly.
Read a post with a list of supplements for Muay Thai fighters to make your training even more effective.
Also take a look at a simple workout plan: Muay Thai workouts and after workout recovery to maximize the gain.