- Analysis of the USDA Cost of Food at Home database shows that fat is the cheapest macronutrient.
- Protein is the most expensive macronutrient, however a reduced carbohydrate diet does not necessarily require an increase in protein.
- Reducing the amount of carbohydrate and increasing the amount of fat in your diet is the most effective way to reduce your grocery bill.
One of the common concerns about eating differently from the norm is that it will be more expensive.
Apparently one of the reasons for the relatively low Recommended Daily Intake for protein of 0.8g/kg is that many people can’t afford to eat more protein.  One of the common criticisms of Paleo or the Banting Diet (LCHF) is that it will be too expensive due to the extra protein. 
To see if these concerns were valid I thought it would be interesting to see what the data has can tell us about the relative cost the three macronutrients, protein, carbohydrate and fat.
The chart below shows the cost per calorie versus the percentage of protein in the thousand or so foods in the USDA Cost of Food at Home database. 
Protein is indeed the most expensive of the three macronutrients. As you move to the right in the chart you can see that your weekly grocery bill will increase.
Average intake of both protein and fat in the United States decreased between 1971 and 2004, with an overall increase in carbohydrate. 
While from a nutritional point of view there area lot of good reasons for people to eat higher levels of protein, a low carbohydrate diet is not necessarily high in protein.
People aiming for therapeutic ketosis may aim for lower amounts of protein to minimise insulin.
Tim Noakes’ Banting diet recommends that people get between 20 and 30% of their calories from protein. He says that those with diabetes and / or insulin resistance issues should aim for the lower end of this range, while people who are active and healthy can aim for higher amounts. 
Practically it is difficult to eat much more than 30% to 35% protein from real foods.
The table below shows the relative change in cost if we were to increase our protein from current average levels back to 1970s levels, or to moderate levels such as the Mediterranean diet or even the higher protein Atkins approach.
|scenario||% protein||cost ($/kcal)||change|
As shown in the table below, the most expensive high protein foods tend to be seafood. For reference, the average cost of food across the more than one thousand foods in the database is $5.37/kcal.
While protein can be expensive there are some low cost high protein options available.
If you are willing to try organ meats you might get them even cheaper as they are often discarded. The cheaper organ meats also typically have a much higher nutrient density than the more popular muscle meats or even fruits or vegetables.
You often hear the term ‘cheap carbohydrates’, but does this mean that a diet of processed grains and sugars is the most economical way to fill your shopping trolley?
While sugar and corn starch are very cheap food ingredients per calorie, the analysis of the data suggest that a higher carbohydrate diet is actually more expensive overall.
The cheaper high high carbohydrate foods tend to be processed and calorie dense. While the most expensive high carbohydrate foods tend to be natural foods that have a much lower calorie density. The table below shows that someone switching from a typical western diet to a reduced carbohydrate diet could make some significant savings.
|scenario||% carbohydrate||cost ($/kcal)||change|
So if increasing the proportion of protein and carbohydrate both increase the cost of our food bill then what makes it cheaper? Yes it’s the other macronutrient, fat.
Increasing the proportion of fat in your diet while decreasing the carbohydrates will make your meals tastier, gentler on your blood glucose and cheaper. Not to mention the fact that people typically spontaneously consume less calories when they consume less carbohydrates.
You may pay a premium for coconut oil, butter or olive oil relative to corn oil which is the cheapest food ingredient, however these fats are still much cheaper than the other macronutrients.
It appears that the it’s the very cheapest ingredients that are so prevalent in processed foods – sugar, corn starch, corn oil, high fructose corn syrup. Regardless of cost you’re always going to have to make a value judgement on the nutritional value of your food.
Increasing the protein content of your diet will increase your grocery bill marginally.
While higher levels of protein may be ideal for people who are healthy and active, LCHF is not necessarily high protein, particularly for those who struggle to regulate their blood glucose levels.
The LCHF approach, with its combination of moderate protein, lower carbohydrates and high fat provides an optimal solution with respect to blood glucose management, nutrition and cost.