The GOMAD diet is not exactly a diet, but actually just a simple instruction.
The only rule of the diet is to drink a gallon of whole milk every day (no, that is not a typo) alongside an individual’s normal meals and snacks.
This strategy is intended to do the opposite of most diets, aiming to put on large amounts of body weight, as opposed to losing body fat. Therefore, it is targeted towards gym go-ers, especially bodybuilders, looking to put on significant amounts of muscle mass in a short space of time.
The GOMAD diet is only meant to be used for 2-8 weeks, however it also instructs people to keep drinking a gallon of whole milk every day until their goal weight is reached.
How Does GOMAD Work?
A gallon of whole milk provides roughly:
- 2,400 calories
- 127 grams of fat
- 187 grams of carbohydrates
- 123 grams of protein
Clearly this amount of calories, especially alongside one’s normal dietary practices, will definitely put on large amounts of weight in a short space of time.
To put this in perspective, eating 500 calories more than you burn per day is estimated to put on 1 pound of bodyweight per week – as 3500kcal equates to 1 pound. Based on this, considering an individual’s previous diet provided enough calories to maintain their weight, the addition of 1 gallon of milk per day can theoretically add up to 5 pounds of bodyweight per week!
The idea of the GOMAD diet is that a significant chunk of this added weight will be in the form of new muscle tissue.
The use of solely liquid calories as opposed to adding whole-foods is based on the idea that liquids will enable people to not feel as full throughout the day compared to solid food. The absence of any type of dietary fiber (an indigestible carbohydrate) in milk also makes it easier to consume, as fiber generally slows down digestion and increases satiety levels from a given meal.
In terms of micronutrients, this amount of whole milk will also meet most of an individual’s daily vitamin and mineral recommendations:
- Vitamin A: 211% of the recommended daily amount
- Vitamin B1: 150% of the recommended daily amount
- Vitamin B2: 507% of the recommended daily amount
- Vitamin B5: 291% of the recommended daily amount
- Vitamin B6: 208% of the recommended daily amount
- Vitamin B12: 731% of the recommended daily amount
- Vitamin D: 332% of the recommended daily amount
- Calcium: 441% of the recommended daily amount
- Magnesium: 93% of the recommended daily amount
- Phosphorus: 468% of the recommended daily amount
- Potassium: 110% of the recommended daily amount
- Selenium: 262% of the recommended daily amount
- Zinc: 131% of the recommended daily amount
Based on this micronutrient profile, that means the only micronutrients one gallon of milk does not cover are niacin, folate, vitamin C, vitamin E, vitamin K, iron, and manganese. Assuming the rest of the diet contains balanced meals, micronutrient concern will certainly not be a concern for anyone trying the GOMAD diet.
Is GOMAD Safe?
Although the consumption of dairy in moderation appears to provide health benefits such as improved bone health, and a reduced risk of cardiovascular disease and mortality  , excess intakes of dairy may lead to a variety of health issues.
The Drawbacks of Doing GOMAD
Below we’ve listed why it might not be such a great idea:
High Intake of Lactose
The sugar contained with milk is called lactose.
As lactose is also prevalent in human breastmilk, babies produce an enzyme called lactase that is responsible for digesting this sugar.
However, at just a few months old, lactase production naturally starts to decrease as babies are gradually weaned off breastmilk.
This production continues to decline into adulthood as a consequence of the normal down-regulation of lactase expression .
In fact, about two thirds of the adult population is defined as being lactase deficiency and therefore will cause difficulties in digesting lactose – the degree of deficiency varies .
When lactose is not able to be digested in the small intestine, it will pass on to the large intestine where it is fermented by various types of bacteria. This process generates a large amount of gas, potentially causing bloating, diarrhea, and stomach discomfort.
An individual’s tolerance of lactose is ultimately dependent on the dose of lactose consumed, lactase expression, transit time in the gut, and the composition of the gut microbiome . Evidence even suggests modest intakes of lactose (~20 grams) could cause anxiety in susceptible individuals 
Most people with lactose intolerance can still tolerate small amounts of lactose (~10 grams), especially when it is combined with other foods or spread throughout the day .
Now considering 1 gallon of milk contains ~150 grams of lactose, it is clear to see that this could cause some serious digestion issues (get ready to spend the entire day in the toilet!)
No Dietary Fiber
Dietary fibers are indigestible carbohydrates that have great influence on intestinal motility and absorption rates of glucose and dietary fat .
Dietary fibers pass untouched through the gastrointestinal tract. Instead, they bind to nutrients and nutrient precursors in the gut to prevent their absorption and slow down the rate if digestion. A lack of dietary fiber may lead to fast rates of digestion and cause diarrhea, especially if liquids are consumed (such as milk).
This is because fiber are required to adequately increase fecal bulk .
Dietary fiber is also necessary for promoting a healthy composition of microorganisms in the gut and protecting the barrier of the gut. A lack of fiber will lead to the production of “bad” bacteria and cause an imbalance to the intestinal flora, thus affecting intestinal function, and resulting in diarrhea and nausea  .
The recommended dietary fiber intakes for adults is 14 grams per 1000 calories. Keeping in mind that 1 gallon of whole milk contains 2,400 calories, it should be expected to contain ~35 grams of fiber – but it actually contains zero!
Excessive Intake of Saturated Fat
Much like dairy, saturated fat can be part of a healthy balanced diet when consumed in moderation.
Recent evidence has even suggested that saturated fat is not as larger health concern as once theorized. Reviews have found that there is not a consistent association between the consumption of saturated fat and inflammatory biomarkers . In addition, not all observational studies have reported significant associations between saturated fat intake and risk of heart disease, stroke, or cardiovascular disease .
However, excess consumption of saturated fat likely does poses some type of health risk.
For example, high intakes of saturated fat is able to increase the amount of LDL cholesterol in the blood . This increases ones chance of developing cardiovascular disease as LDL is the substance that attaches to the lining of arteries, increases inflammatory responses, and results in plaque formation on arterial walls .
In addition, chronic intakes of saturated fat may lead to lipotoxicity – defined as an accumulation of fatty acids, or derivatives, in non-adipose tissue which causes cellular dysfunction and death.
Fat tissue also has a limited storage capacity for free fatty acids, and high fat diets can cause these stores to become overloaded. This condition has been recognized as a contributing factor to the development of diabetes, due to the death of β-cells that are usually responsible for producing insulin – described as lipoapoptosis .
For these reasons, the American Heart Association recommend not to consume over 5% of total daily calories from saturated fat. However, 1 gallon of whole milk provides 2400kcal, and ~25% of these calories are coming from saturated fat!
Is GOMAD The Best Way To Gain Weight?
As well as the health concerns, there is simply no need to be consuming 2,400 calories above one’s normal calorie intake in order to gain weight.
Seen as the goal of the diet is to gain muscle mass, not fat mass, it should really recognize that more calories are not necessarily better.
With the estimate that humans cannot build more than 1-2 pounds of muscle per month, a diet which aims to put on up to 5 pounds of body weight per week will undoubtedly result in excessive fat gain in a short period of time.
A more reasonable caloric surplus of between 250-500 calories is recommended for those wanting to build muscle without adding excessive amounts of body fat. This is approximately an additional glass of whole milk per day, not a gallon!
The GOMAD diet is aimed at fitness enthusiasts looking to gain large amounts of muscle in a short space of time. It instructs them to drink an additional 1 gallon of whole milk on top of their normal diet.
Such an eating plan will not only cause excessive increases in fat mass, but it is also a large health concern in regard to digestion issues and increasing cholesterol levels.
For these reasons, the GOMAD diet is not recommended for use, and those wanting to add muscle mass should look to less extreme dietary methods to achieve their goal.