Food habits, state of mind does influence our intelligence. One should be aware of this knowledge and also self analysis at present situation. Awareness it self is knowledge and intelligence.
Let's discuss some such daily situations; in morning hours I was working quite hard and work was primarily lot of thinking; so my brain consumed oxygen and sugar in same proportion. My intelligence at this level is relatively dulled and needs pampering. If the food available is what I like then such food not only provides nutrition and calories to my brain but it supplies joy by stimulating my satiety centre thus providing add on energy to brain , this is subtle energy but it's very powerful too.
So my intelligence illuminates with more perception power and more expression power! Mind one thing here, your favourite food must not be fast food but wholesome meal is important. Once in a while fast food does provide this magical effect, but not always. Otherwise, make balance meal as your favourite food; since mind can be trained, one can inculcate such positivity.
Now let's talk about mind sate and it's relation with intelligence. When I am doing (working on) my favourite project, then I am more focused, my creativity is at it's optimum best, my perception and acceptance is wider and more importantly I can do more qualitative and quantitative work at less physical and mental energy consumption so my total energy is conserved. Sometimes I gain more energy in such favorable situations. Say , when you can complete your project in time with maximum accuracy then you feel satisfied and feel more energetic. This is subtle fact that satisfaction does restores energy pool. In such intellectual phases, Indian Philosophy states that your Mann and Buddhi are in harmony with Cosmic Thinking Bank and Universal Power Store so this link provides you new ideas, more vitality , more enthusiasm and glimpses of wisdom. The secret here is Your Creativity links you with Power of the Creator itself! Of course, it's your choice to believe and accept this Fact or not. I leave it you . But experiences and theories have proved one thing that if your profession is according to your nature( Swabhav) , likings capacity then you can earn name, fame, success, money and Bonus Mental Peace and Physical Health.
Else just try to blend your mind in liking the field, you are working in, now. Though it generates friction initially, mind can be trained with self confidence and expert guidance. But mind it, that favourable mind state helps easy and powerful flow of creativity, and lead to personal as well as cosmic benefits.