Is eating a varied diet actually better & why?

Answer

Qualifications to answer this question: MIT graduate, NSF PhD scholar at the Turnbaugh lab (UCSF)
So long as it is baseline “healthy diet” (eg a focus on whole foods/ high in nutrient-dense components), yes! Here’s why:

1. It benefits your microbiome (e.g. the bacteria living in your gut, which have a profound influence on the health of the whole body). For example, the American Gut Project, a study which leveraged data from >10,000 citizen scientists to study the microbiome, found that people who ate >30 different plant foods (eg grains, fruits, vegetables) every week had more diverse gut microbiomes compared with people who ate 10 or fewer (a more diverse microbiome is generally seen as beneficial). Furthermore, those consuming >30 different plant foods had more bacteria that produce beneficial metabolites known as short-chain fatty acids.
2. A varied diet increases the likelihood you will fill dietary nutrient gaps. This is fairly intuitive, but for example, see this study from the American Dietetic Association
3. Generally, a varied diet is more pleasurable! Studies suggest that novelty and variety are key drivers for enjoying food…that said, increased pleasure is often tied to increased consumption (this has been found within eating occassions/meals particularly) so this should be monitored. See 1, 2, and 3.

Hopefully this was some help! Of course, everybody is different in terms of nutrient needs and preferences. Further, there are many levels at which variety can be implemented (eg within meal, within day, within week). My advice is to consider the weight of the evidence, learn more, and if you see fit, start adding some variety to spice up your life (forgive the lame pun!)

Answer

It is a rule of thumb for the typical human. The more diet variety you have, the more chance you have of consuming a range of nutrients and thus, reducing your risk of becoming deficient in something. If you are in the 5% of the population who is able to consume a fixed but nutritious diet on the regular, then I don’t see why you would need to mix things up. Though you should probably familiarise yourself with RDAs of different nutrients to ensure you don’t miss something when planning your dietary pattern

Answer

Rather than overcomplicating it. Eat whole foods, eat similar to your greater ancestors.

Scotland natively only grew meat, eggs, milk (and fermented dairy), barley, oats, carrots, potatoes (occasionally), apples, berries (exclusively in spring and summer), and some other small bits. We didn’t have a wide variety. Legitimately, no country has that wide a variety of food. Logically, there’s no sense to it.

Just stick to eating whole foods. You don’t need variety. There’s also little evidence that it helps longevity, since food diversifying is extremely new. So that’s instantly dismissed.