If calories are king why does it matter what my macros are? Or, in other words; If calories are king why does the composition of my diet matter?
There are 2 main reasons (..or possibly just 1 absolute reason):
1) Essential nutrients
You NEED certain essential amino acids that make up protein and essential fatty acids that make up fat from your diet as your body cannot synthesise these. You also need a supply of vitamins and minerals for your body to function. A varied diet that includes fat, protein, vitamins and minerals gives your body the nutrients it needs to survive and maintain health.
2) Satiety and adherence
You will struggle to stick to a diet that isn’t well balanced.. this is a much lesser point than the first one as people can and do stick to very restrictive diets e.g very low carbohydrate diets, vegan diets or keto diets. However, these diets do have a higher occurrence of deficiencies and if you did decide to follow these you should consider supplementing with nutrients you may be missing. E.g. vitamin b12, calcium, iron and zinc in vegetarians and vegans.
Now I am side tracking back to my original point.. maybe there is only one real reason but my point here is it probably isn’t enjoyable or maintainable for most people to stick to restrictive diets that cut out large parts of a balanced diet long term. Once you have accounted for essential levels of fat, protein and (I would suggest) fibre the rest is up to you/preference.
Note that you will probably have at least some carbs if you meet a decent fibre amount and do not want to rely solely on supplements for vitamins and minerals. You can and will lose weight in an energy deficit no matter what your diet’s macro nutrient composition is.
In fact, we probably over play our need for a ‘healthy’ diet to maintain health. Especially in those who have a lot of fat to lose. Their loss of fat is going to improve their health to a bigger extent than any slight deficiencies they may or may not encounter.
Examples of this include:
The obese man who fasted for over a year, experienced no ill health and only took vitamin and potassium supplements.
And more recently..
The man who went on a convenience store diet AKA the twinkie diet and experienced an improvement in health markers due to his fat loss despite the fact his diet would be classes as ‘unhealthy’ and lacking in nutrients. In fact, Twinkie diet man lost 27lbs in 10 weeks and more importantly his health markers including cholesterol and blood glucose levels improved.
Note that he also took a multivitamin and protein shake and as well as occasional canned veg.
One more example is the Newcastle diet which puts overweight, type 2 diabetics on a very low calorie diet of just 600 calories a day made up largely of a high protein, high sugar meal replacement shake and a salad.
This diet has consistently shown the ability to reverse type 2 diabetes by reducing fat around the pancreas and liver and restoring normal glucose control (more on this here).
Although I am in no way suggesting the diet above I think it is a useful observation and proves the point that if you have a lot of fat to lose fat loss has more benefits to health than diet composition per se. i.e
“When you lose fat, regardless of how you’re doing it — even if it’s with packaged foods, generally you will see important health markers improve.