Dr. Brewer no doubt did a lot of research on nutritional links to prenatal health.  He was a wise man to stress the importance of nutritional intake to prevent complications.  However, it is important to keep a few things in mind if advocating his specific diet plan... such as actually knowing what you're advocating, believing in what you're advocating, and being open to changing what you advocate.  There was a time where I advocated the Brewer diet... but this isn't necessarily the case anymore... and here is why:

1. Although the actual diet plan lays out various food groups, the "most important aspects" are said to be high calorie, unrestricted salt and water, and 80-120 g of protein daily.  What do pregnant women do when they hear this?  What do birth advocates do when they hear this?  It's aaaallllll about the protein and its rarely about where the food comes from, even though a more specific diet plan is laid out in Brewer's guidelines.  Eating a 10 ounce steak or drinking a quart of milk is not a wholesome meal.  If you want people to eat better, you have to teach them how to eat.  We know that high meat diets are not the best for overall and long-term health... especially red meat.  We do know that those that eat meat sporadically have similar health outcomes as vegetarians.  It's the vegetables and fruits...plants... that do the most to heal and nourish the body.
2. Brewer lived in a time where dairy was thought to be a necessary part of the American lifestyle.  The government pushed milk as an adequate way of getting nutrients to families.  It was often inexpensive.  But, let's keep in mind how unnecessary dairy is in our diet.  Edible?  Yes.  Yummy?  Yes.  Addictive?  Yes.  Nutritious?  It can be, but certainly not in excess.  Dairy can cause the basic digestive problems most know about, but it also increases mucous in the body making allergies more prevalent and exacerbating other common ailments seen in our culture.
3. Brewer also lived in a different time...  Pesticides weren't as highly used as they are today.  Gardens were more abundant post-depression era.  Lifestyle was less sedentary.  The overall food choices were simplifying with packaged meals, but they still weren't to the level they are today.  People were using the animals down to the bones to make nutritious and healing broths, though this was just a necessary part of life at that time.  Though the generation was seeing the start of the convenience foods, there were still many wholesome options available, .  Studies show of all diet plans, the ones that follow whole real-food guidelines show similar health outcomes.  It is the REAL food that matters most.  I'm not so sure the specifics of the "diet plan" helped his patients, or the fact that they were eating real food made his clients healthier.  But, this is still different from "high calories and high protein."
4. Dark leafy greens are abundant in nature.  Although every other fruit, vegetable, and animal peaks in abundance at various times throughout the year... dark leafy greens are available in every season.  Is there any wonder why?  Of all the foods, dark greens are the most nutrient-packed with high bioavailability.  They give us wonderful amounts of calcium.  They give us wonderful amounts of folate (the natural and needed form of folic acid).  They give us vitamins that nourish our skin and help it flex and heal.  They not only cleanse the blood of toxins, but they also build blood to the 50-60% increase needed during pregnancy.  They are the healing herbs used most often.  It is very true that we need a balance of protein and calories in our body.  Protein builds cells, too and is important.  But understanding that when you eat vegetables, you can eat a LOT more than when you eat meat you can get a lot of protein from dark greens and a rainbow of colors.  This not only digests more easily and offsets nausea, but builds your blood.  (Did you know the only difference in the molecular structure of hemoglobin and chlorophyll is the center iron atom?  Chlorophyll, found in dark greens, is amazing at building blood levels... a life source of plants, and people).  We need a lot of dark leafy greens, and a balance of colorful other vegetables and fruits.
5. People don't soak grains, beans, and legumes much any more.  Even if they are soaked, they're rarely sprouted.  The fact that more nutrients is released from all of these plant-growing foods when they are actually in their grown form indicates just how important a plant-based diet is.  It is also interesting that the "fruit" of these plants are also the seeds of these plants because they take so much work to utilize, but store very well.  Whole grains are a big focus in the western culture, but it doesn't do much good if they have high amounts of digestion-irritations, and can't release much of their nutrients because they aren't in their nutrient-releasing stage of growth.  Not to mention all the foods that have additives for preservation of these grains that overload our bodies and cause complications like ADHD, gluten intolerance, skin disorders, digestion problems...etc.  They have certainly been staple - filler - foods in many cultures, but are often seen at times where other food sources are low, whether famine or season.  These plants have nutrients, but too much of anything - especially if not prepared in the right way and genetically altered to produce certain cooking properties - is not good.  There are so many preservatives on our foods these days that we are getting these sources even when we don't know it, and it is damaging our health.  Everything in moderation.

So, thinking about a difference in culture of now and then, there is much more to teaching a mother - a family - how to eat.  Thinking of how your food arrives on your plate - from nature (or farm) to the store, to your house, how you prepare it.  It does matter.  The easiest way to get a wholesome variety of nutrients is to eat foods as close to nature as possible.  Not only in where they come from, but mimicking what you actually would have access to if you were foraging throughout the seasons and stores weren't so accessible.  Greens would be abundant in every season.  Meat would be available occasionally.  In the spring, you would have foods that increase the toxin-releasing properties in your body.  Then you would be met with luscious arrays of colorful fruits and vegetables that provide you with many vitamins and minerals that increase your health and last throughout the cooler months.  Beans and grains are then available and store well through the dormant season followed by those cleansing foods again whenever they're available.  And, you may very well be gestating based on the seasons as well.

You would not be bound to one type of food or color, but see a mixture of wholesome variety on your plate.  A plant-based lifestyle with greens as the foundation, a rainbow of fruits and vegetables, then meats and grains and legumes enhancing your meal.  Everything in moderation, even when it appears to be healthy.  No need to count calories or protein.  No need to count cartons of milk.  When a market is accessible to you, imagine it as your forest and buy like you were picking fresh off the vine.  This isn't a "pregnancy diet."  This is a lifestyle choice and a way of seeing what you put in your body.  When a woman eats healthy, she does nothing different during pregnancy other than eating more.  She would already be eating (or drinking) nourishing herbs.  She would already be eating high calcium and folic acid meals.  She would already be eating detoxifying plants and a variety of vegetables and fruits.  This continues while breastfeeding and through every stage.  You create a lifestyle, not a 9-month diet plan of checking off nutrients.