What you eat impacts your mood. An explanation:
The first image shows how various foods impact your blood sugar levels. Notice that fat is least likely to promote blood sugar, protein is second and carbohydrates are far and away the most likely. Also, note the quick rise and fall of blood sugar as promoted by carbohydrates, in contrast with more sustained curves for protein and fat. This is important, as the steep, quick curve of carbohydrates can promote mood swings.
The body makes insulin in response to a rise in blood sugar. Insulin controls blood sugar, and prevents it from getting too high. Insulin is a storage hormone that turns blood sugar to fat.
The second and third graphs illustrate the story of insulin, blood sugar and mood swings.
The second graph illustrates ideal fluctuations in blood sugar, along with insulin. For health, you should not sustain blood sugar or insulin that is too high. In general, to achieve this ideal trend it is best not to eat highly refined carbohydrates (sugars and starches that spike blood sugar--see the first chart), and to eat adequate fats (which have little effect on blood sugar, also illustrated on the first chart). Eating this way creates a buffer against stress, keeping hunger at bay while promoting an emotionally smooth day and amiable mood.
To be clear, sugar is not the only sugar in our diet. Grain flours and their products turn to sugar in your digestive system, and enter the bloodstream as glucose. Examples: An unsweetened bowl of cornflakes is a bowl of sugar (glucose); a bag of bread is a bag of sugar; a bowl of oatmeal is a bowl of sugar; a plain bagel is a bolus of sugar, etc. Fruits of all kinds, tropical fruits in particular (bananas, e.g.) contain sugar. Dates and raisins are high in sugar. Milk sugar (lactose) is sugar. Sugar, sugar, sugar... I think you get the picture.
The third chart applies to the a Standard American Diet (SAD), a 55-65% carbohydrate diet, much of this composed of processed foods, refined starches and both natural and added sugars (see the sugar examples in the paragraph above). See the yellow area under the curve? That is excess blood sugar. If this gets high enough it could put you in a coma.
Fortunately, the human body has a strategy to avert this danger: insulin to the rescue! Insulin whisks away excess blood sugar, helps convert it to fat then locks it safely away in your fat stores.
But, while it saves your life, there is a downside to this 911 system. When a surge of insulin kicks in there is a rapid decline in energy, resulting in hunger, often accompanied by anxiety, headaches, irritability and other symptoms. You may feel "hangry" (hungry and angry). You need fast relief. You grab the nearest refined starch or sugar (bagel, e.g.), and up goes your blood sugar. You feel better for a time,then the cycle starts over again.
Folks who eat this way complain of frequent bouts of hunger, mood swings, irritability, poor concentration, anxiety, panic, post-meal drowsiness and "brain fog" during the day. Over time there is stubborn weight gain. This high refined carbohydrate diet can be a disaster for the brain. Eat this way often enough over decades and you could become demented (Alzheimer's, aka Type III Diabetes).
So, which of the last two graphs is yours? If giving up refined grains (including whole wheat breads), cereals of all kinds, and sugars while eating more fat could help improve your mental health, would you do it?