The ketogenic diet, more commonly referred to as the “keto diet”, is one of the most popular diets for weight loss right now. This very low carb eating plan promises rapid and dramatic weight loss to its followers. However, medical experts remain dubious about its safety and efficacy. So are the keto diet and phentermine weight loss pills a good combination? Here we’ll discuss the keto diet: its origins, pros & cons, and the advisability of combining phentermine and low carb or fad diets.
REMINDER: We’re not doctors and no part of this post in any way constitutes medical advice, nor an endorsement of using the keto diet and phentermine together. This post is purely informational. Always speak with a licensed medical professional before undertaking any major dietary change.
What is the keto diet?
The popular keto diet is a very low carbohydrate, moderate protein, high fat diet. There are several variations of this latest fad diet, but the “standard” keto diet calls for a distribution of 75% fat, 20% protein and 5% carbs. This means that just 5% of daily calories come from carbs – that’s just 75 calories (about 19g of carbs) for a person eating 1500 calories per day!
There also exist several other variations of the keto diet including the: high-protein ketogenic diet (60% fat, 35% protein, 5% carbs), cyclical ketogenic diet (5 days on, 2 days off) and targeted ketogenic diet (eat more carbs around workouts). The last two are primarily designed for athletes have not been extensively studied. 
However, not everyone needs to restrict carbs quite this much. Many people can achieve a state of ketosis by eating anything less than about 50 grams of net carbs (total grams of carbs – total grams of fiber) per day. Other low-carb diets that are still colloquially referred to as “keto” allow for still higher levels of daily carbohydrate.
Where Keto Came From
The ketogenic diet was originally developed as a treatment for refractory pediatric epilepsy, or seizure disorders in children that aren’t successfully controlled by medications. Since this diet forces the brain to shift towards using ketone bodies (from fat) instead of glucose (from carbs) as its primary energy source, adhering to a keto diet can help reduce seizure frequency and severity. The strictest clinical patients follow a 4:1 keto diet wherein they get 80% of calories from fat (ideally MCTs, which are more ketogenic) and only 20% of calories from protein & carbohydrates. The clinical goal of this diet is to provide just enough protein and calories to support sufficient growth and weight status, while absolutely limiting carbohydrate intake to reduce epileptic symptoms.
Medically, epilepsy management remains the only widely-accepted use of the ketogenic diet. Scientists are researching the diet’s effectiveness in treating or managing other neurological disorders and cancer, but so far there’s no conclusive evidence to support the implementation of this diet to treat or manage these conditions. 
How the Keto Diet Works
The basic idea behind the keto diet is to drop your intake of carbohydrates so low that your body and brain switch to ketone bodies as their main source of fuel.
Fueling Your Body on a Balanced Diet
Under normal conditions, the body relies on glucose as its primary source of energy. Glucose, or sugar, is the most biologically-available source of fuel and it’s our brain’s favorite food. When we’re eating a normal, balanced diet about 50-60% of our calories come from carbs. Grains, fruits, vegetables (especially starchy vegetables like potatoes, corn and peas) and dairy products contribute to your daily carbohydrate intake. Sugar – whether it’s white sugar, brown sugar, honey, maple syrup or agave – is also digested as a simple carbohydrate. When we ingest carbs, we use insulin to break down sugars in our foods and convert it them into glucose that our cells can use for energy. This is how someone eating a balanced diet gets most of their energy, and the quick turnaround of glucose metabolism is why it’s normal to feel more energized soon after eating and then start feeling hungry a few hours later.
Fueling Your Body on Keto
However, when the body doesn’t receive enough calories or carbs (or can’t use them, in the case of uncontrolled diabetes), the liver starts synthesizing ketone bodies to fuel the body and brain. These molecules, which are derived from fatty acids, serve as an efficient fuel substitute for the missing glucose. The high-density nature of ketone energy may explain (at least partially) why a true keto diet proves neuroprotective against seizures and other neurological conditions.  Ketone tests and keto strips determine if a person is in ketosis by measuring the levels of ketone bodies in their blood, breath or urine.
Potential Benefits of Keto
Proponents of the keto diet note many possible advantages of following this restrictive regimen. The most-touted benefits are rapid & dramatic weight loss and lower insulin levels over the short-term.
Adopting a ketogenic diet allows followers to lose weight quickly and without counting calories. Many people report they feel less hungry while in ketosis, especially after the initial transition period. More, studies show that adults lose more weight following a high-fat/low-carb diet instead of a low-fat diet.   However, experts note that much of this initial weight loss is simply water weight due to the drop in glycogen.
A very small study (of 12 people) also indicated that the ketogenic diet could reduce insulin sensitivity. This effect would reduce risk for developing type 2 diabetes and contribute to the management of several other conditions like metabolic syndrome and PCOS. 
Still, many health professionals warn that the risks of this extreme diet outweigh any potential benefit.
Possible Risks of Keto
The long-term side effects of using ketosis for weight loss have not been studied, nor has the combination of the keto diet and phentermine weight loss pills. There’s not enough evidence to determine if this diet is safe for everyone, and health experts warn that the restrictive plan can do more harm than good (especially when it’s not medically-supervised).
Common side effects of the keto diet include constipation and dehydration (two problems already experienced by many phentermine users), as well as electrolyte and micronutrient deficiencies. This diet may also increase the risk of kidney stones (especially worrisome for Qsymia users), gallbladder problems, bone fractures and/or menstrual irregularities. 
Long-term studies of children who use follow keto diets for seizure control also exhibit higher total cholesterol and LDL (bad cholesterol) levels. While keto proponents claim this diet improves heart health, long-term research indicates that it worsens patients’ lipid profiles.
This forum user and multiple registered dietitians also warn that entering ketosis weakens muscle development, including in the heart. The heart is the most important muscle in the body and weakening it could prove extra-problematic for phentermine patients. 
If you are taking Qsymia, do NOT start a low-carb or ketogenic diet. The topiramate portion of this medication is an anti-seizure medication that should not be combined with any sort of high-fat, low-carb diet like Atkins or keto. 
Keto Diet and Phentermine
While many people adopt the keto diet to lose weight quickly while taking phentermine, this fad diet is NOT a good choice. Medical experts warn that this diet does more harm than good, plus its potential interaction with phentermine remains unknown.
Problem 1: Keto isn’t proven (or even tested) for use alongside phentermine
Evidence does not yet support the keto diet as an alternative or addition to pharmaceutical therapy for weight loss. The long-term effects of ketosis for weight loss have not yet been studied and there is not sufficient evidence to suggest it is safe for everyone. In fact, some evidence indicates that it could prove dangerous.  Never follow keto, Atkins, or any other low-carb/high-fat diet while taking Qsymia.
Problem 2: Keto isn’t a sustainable dietary pattern
Moreover, research repeatedly shows that the most effective diets for weight loss are the ones we can stick to long-term. Very few people maintain a super-restrictive eating plan like keto for years at a time. It is much more commonly used as a temporary diet that people stop following as soon as they reach their goal weight. Unfortunately, the problem with radical fad diets like keto is that, in most cases, the weight starts to come back as soon we start eating normally again. This is especially true with keto given that much of the initial weight loss can be attributed to a loss of water weight.
Problem 3: Keto undermines your opportunity to develop healthy habits while taking phentermine
Finally, using the keto diet and phentermine together takes away a major advantage of your prescription. Phentermine is a powerful drug to help jumpstart your weight loss, but the idea is that this prescription medication acts as an addition to overarching lifestyle changes. It’s important to use your three months on phentermine to establish healthier eating and exercise habits for life. It shouldn’t be a “one and done” twelve week commitment that you abandon once you reach your goal weight. Since the keto diet isn’t a sustainable eating plan, this need for a long-term weight loss mindset is another reason that it’s not a good choice to do the keto diet and phentermine together. Instead, practice consistent dietary balance and portion control to set yourself up for long-term weight loss success!
If you still want to eat low-carb or keto while taking phentermine, discuss it with your doctor and a registered dietitian first. Severely limiting or eliminating entire macro groups (in this case carbohydrates) is hazardous even for the healthiest people, and the risk increases when you have other conditions. This potential danger is compounded by combining a strong prescription medication like phentermine (or worse-yet Qsymia) with the restrictive diet. As a result, it’s critical that you speak with your doctor before making any radical dietary changes.
Do you use the keto diet and phentermine together? Share your questions and comments with us in the comments section below!
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